Hi All,
The numbers I quoted for Zenith 30VM-5 carbs fitted to Javelin's and Jupiter's came from Zenith's own current technical website. I would be wary about other numbers, as these may fit and look similar, but might not operate as Zenith's intended?
All the best,
David
Carbs
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David Morris
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Keith Clements
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Re: 30 vm carbs.
It is likely the set up of the carbs done in 1950 was not that exact or highly tuned and probably has little relevance to modern petrols or even the developments that have taken place in other areas such as the gas flowing of the combustion chambers.
Even if you have an unworn carb, experience has shown that different jet sizes than those in the Zenith spec give better performance.
But most Jowett owners just want the cars to idle well and give enough power to get along without sooty plugs or overheating.
Getting the carburation so there are no flat spots and high rev power is the icing on the cake.
Note that jets also wear and passageways get restricted so diverging from the original spec.
Even if you have an unworn carb, experience has shown that different jet sizes than those in the Zenith spec give better performance.
But most Jowett owners just want the cars to idle well and give enough power to get along without sooty plugs or overheating.
Getting the carburation so there are no flat spots and high rev power is the icing on the cake.
Note that jets also wear and passageways get restricted so diverging from the original spec.
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Barry20383
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Carbs.
Is it wise when fitting the carburettors to use gasket cement on the gaskets to be sure of a good seal.
Thanks Barry.
Thanks Barry.
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Nick Webster
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Re: Carbs.
Usually with carbs it is not neccessary. Depends partly on what type of gaskets you have. The sort that almost have a plastic sheen on them certainly don't need goo. What is more relevant is checking the flange face is true. VM-5 carbs are particularly prone to the flanges distorting, apparently pulling down either side where the bolt holes are. Check them against a piece of glass so you can see if they touch all the way round. If you are not happy with them the usual way of correction is not to take a file to them but put grinding paste on the glass and grind the face flat. Needless to say clean off the paste very carefully afterwards. Check the spacers between carb and head are flat faced too.
Nick
Nick
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Nick Webster
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Re: 30 vm carbs.
Some more about this subject that may be of interest. I am currently working on a car that has been plagued with a dreadful flat spot on engine pick up. It has changed hands a few times since rebuild and there is some email paperwork that reveals that this seems to have always been a problem. I managed to adjust the carburettors so that the tick over was comparatively slow, but this resulted in settings which I would normally expect to result in the engine going so slow it would stop. Furthermore the flat spot has persisted.
The carburettors were reconditioned units but I became suspicious and decided to strip them down. The throttle spindles had been built up for wear and then turned down to size. Actually they were about 0.2mm oversize and would not fit in another carburettor with original spindles. Very careful examination revealed that with the butterflies in the shut position both the progression jet outlet and the vacuum advance take off were not properly covered by the disc and were in fact open to the engine side of it. Both carburettors were like that. This meant that on tick-over the slow running jet was being supplemented by the progression jet and the engine was at maximum vacuum advance. The likely scenario then was that with the opening of the throttle and the change in depression at that area, both these features would tend to operate in the opposite way than intended - with the resultant flat spot.
At first I considered that the very slight oversize on the spindles might be to blame but by loosening the fastening screws I was able to shuffle and seat the throttle disc so that it sat in the proper position in relation to the drillings. Unfortunately it may be that the discs had been filed slightly because with the holes covered I was not too sure the disc was a good fit against the other side of the venturi. For this and other reasons relating to these carburettors I decided it would be best to start from scratch and went for my pile of spares, that I confess, I had never counted before.
There were two of the late 30VM that I am saving for a rainy day and sixteen VM-5. I sorted through them and with this thread in mind, made a note of the "C" or contract number. It turns out they are a pretty even spread of C1161M and C1334M. And no other number - which was quite a surprise. C1334 does not appear in the Australian JCC lists of Zenith fitted but I have a whole pile of them here! In my time I have had two or three Javelin engines that were Jowett Engineering reconditioned units (i.e. after the factory closed) and possibly they used "C" numbers that were not around when the Javelin was in production. Incidentally, although the 30VM, a generally better design can be found on Javelins, I suspect that in general it would have been reserved for Jupiter reconditioned engines.
There appears to be no functional difference between the C1161 and C1334. The latter is drilled for two screws that in some applications support a metal bracket. This resulted in the requirement to move the Zenith logo to a different spot. What is not identifiable by any reference number is whether they are for mounting on the nearside or offside (where there is provision for the vacuum advance). You have to use your eyes. In my collection some were drilled for the vacuum tube, some not. Some were drilled and then a brass screw plug inserted so that it could be used on the nearside of the engine. It has to be said that given the criticality of the position of the holes relative to the throttle butterfly, you are better off plugging carburettors that are already drilled rather than trying to put holes into one that does not have them.
I have taken a deep breath and bought two new spindles - even the man on the phone remarked about the price. Perhaps this is why people try and reclaim them. They have turned out to be an absolutely perfect fit in my project carburettors with no slack at all. Once again I had to carefully juggle the butterfly disc to the right place. I am rebuilding a pair of C1334, mostly because I have a pair with unworn spindle holes and a plug in the blank spindle end. I think this desirable because it excludes dirt and air. The downside is that it is not possible to regularly lubricate that end of the spindle. The jury's out on what is most important. (Some days later - Edit. I have discovered there is a lubrication hole for the spindle which is accessed by taking the float chamber off, which reveals a very small hole below the slot where the "beak" goes through and just above where the spindle is. This is the oil hole. Not very easy but Zenith did at least think of it.)
I have always bought carburettor parts individually rather than a kit and thus have no knowledge of whether the kits include any kind of instructional hints and tips. In general everything I have read rather concentrates of the correct setting and balance - probably assuming the carburettor is assembled properly. I can only stress how important the setting of the butterfly disc is in correct operation.
Work is on going with other jobs, so I am not able to report a road test by way of conclusion at the moment. One thing that I also have suspicions about is whether the distributor is sticking in various positions of advance. I shall likely do a road test first before changing to a 25D Distributor which in my opinion has a centrifugal advance mechanism superior to the DM2.
Nick
The carburettors were reconditioned units but I became suspicious and decided to strip them down. The throttle spindles had been built up for wear and then turned down to size. Actually they were about 0.2mm oversize and would not fit in another carburettor with original spindles. Very careful examination revealed that with the butterflies in the shut position both the progression jet outlet and the vacuum advance take off were not properly covered by the disc and were in fact open to the engine side of it. Both carburettors were like that. This meant that on tick-over the slow running jet was being supplemented by the progression jet and the engine was at maximum vacuum advance. The likely scenario then was that with the opening of the throttle and the change in depression at that area, both these features would tend to operate in the opposite way than intended - with the resultant flat spot.
At first I considered that the very slight oversize on the spindles might be to blame but by loosening the fastening screws I was able to shuffle and seat the throttle disc so that it sat in the proper position in relation to the drillings. Unfortunately it may be that the discs had been filed slightly because with the holes covered I was not too sure the disc was a good fit against the other side of the venturi. For this and other reasons relating to these carburettors I decided it would be best to start from scratch and went for my pile of spares, that I confess, I had never counted before.
There were two of the late 30VM that I am saving for a rainy day and sixteen VM-5. I sorted through them and with this thread in mind, made a note of the "C" or contract number. It turns out they are a pretty even spread of C1161M and C1334M. And no other number - which was quite a surprise. C1334 does not appear in the Australian JCC lists of Zenith fitted but I have a whole pile of them here! In my time I have had two or three Javelin engines that were Jowett Engineering reconditioned units (i.e. after the factory closed) and possibly they used "C" numbers that were not around when the Javelin was in production. Incidentally, although the 30VM, a generally better design can be found on Javelins, I suspect that in general it would have been reserved for Jupiter reconditioned engines.
There appears to be no functional difference between the C1161 and C1334. The latter is drilled for two screws that in some applications support a metal bracket. This resulted in the requirement to move the Zenith logo to a different spot. What is not identifiable by any reference number is whether they are for mounting on the nearside or offside (where there is provision for the vacuum advance). You have to use your eyes. In my collection some were drilled for the vacuum tube, some not. Some were drilled and then a brass screw plug inserted so that it could be used on the nearside of the engine. It has to be said that given the criticality of the position of the holes relative to the throttle butterfly, you are better off plugging carburettors that are already drilled rather than trying to put holes into one that does not have them.
I have taken a deep breath and bought two new spindles - even the man on the phone remarked about the price. Perhaps this is why people try and reclaim them. They have turned out to be an absolutely perfect fit in my project carburettors with no slack at all. Once again I had to carefully juggle the butterfly disc to the right place. I am rebuilding a pair of C1334, mostly because I have a pair with unworn spindle holes and a plug in the blank spindle end. I think this desirable because it excludes dirt and air. The downside is that it is not possible to regularly lubricate that end of the spindle. The jury's out on what is most important. (Some days later - Edit. I have discovered there is a lubrication hole for the spindle which is accessed by taking the float chamber off, which reveals a very small hole below the slot where the "beak" goes through and just above where the spindle is. This is the oil hole. Not very easy but Zenith did at least think of it.)
I have always bought carburettor parts individually rather than a kit and thus have no knowledge of whether the kits include any kind of instructional hints and tips. In general everything I have read rather concentrates of the correct setting and balance - probably assuming the carburettor is assembled properly. I can only stress how important the setting of the butterfly disc is in correct operation.
Work is on going with other jobs, so I am not able to report a road test by way of conclusion at the moment. One thing that I also have suspicions about is whether the distributor is sticking in various positions of advance. I shall likely do a road test first before changing to a 25D Distributor which in my opinion has a centrifugal advance mechanism superior to the DM2.
Nick
JCC Member
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Barry20383
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Carbs
On checking my carbs i found that the drivers side choke spindle has a lot of play in it . Is this normal as i have recieved re con carbs from jcs and it seems the same on the re con ones as well.
Thanks Barry.
Thanks Barry.
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Forumadmin
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Re: Carbs
It is normal but not as new. It should not really affect carburation except a slight weep on full choke that I doubt would be enough to fail to start the car.
Before you fit the recon carbs it is a good idea to look down the barrel with the throttle closed and see if you can see any light.
It is very difficult to get a new butterfly and spindle to seat properly in an old barrel.
I now put the old butterfly back as it has already bedded in, but even then the positioning on a new spinlde may need some fettling.
Do not assume this has been done as part of the recon.
The old butterfly may also have worn itself into a non-central position if the previous spindle had been worn for a long time.
So in this case better and easier results can be acheived by silver soldering the old spindle and lapping in.
It all depends on the state of the carb before recon. Every one will be individual.
A possible problem with an old (or new butterfly) in a worn barrel is that the relative position of the metering holes will have changed. So do not expect good as new after a recon, but it should be better than it was.
Before you fit the recon carbs it is a good idea to look down the barrel with the throttle closed and see if you can see any light.
It is very difficult to get a new butterfly and spindle to seat properly in an old barrel.
I now put the old butterfly back as it has already bedded in, but even then the positioning on a new spinlde may need some fettling.
Do not assume this has been done as part of the recon.
The old butterfly may also have worn itself into a non-central position if the previous spindle had been worn for a long time.
So in this case better and easier results can be acheived by silver soldering the old spindle and lapping in.
It all depends on the state of the carb before recon. Every one will be individual.
A possible problem with an old (or new butterfly) in a worn barrel is that the relative position of the metering holes will have changed. So do not expect good as new after a recon, but it should be better than it was.
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Barry20383
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Re: Carbs
I assumed the spindles would be blushed if worn. I don't know weather to fit them as they are as worn as the old ones.
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David Morris
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Re: Carbs
Hi Barry,
You mention the choke spindles, which are not really critical. As Keith says, you can get away with quite a lot of play here and she will still start OK. The much more critical spindles are those in the running venturi. After being reconditioned, I would expect these spindles to have been replaced and probably fitted with new bushes in the castings. The butterflies should also have been replaced. That is the normal method of reconditioning worn carburetors. If there is any appreciable wear, its worth checking with the suppliers, just in case yours have somehow slipped through the post reconditioning inspection process.
However, before fitting its always best to hold the reconditioned carbs up to the light and check that the butterflies are closing properly and that there is no slop in the main spindles.
All the best and stay safe,
David
You mention the choke spindles, which are not really critical. As Keith says, you can get away with quite a lot of play here and she will still start OK. The much more critical spindles are those in the running venturi. After being reconditioned, I would expect these spindles to have been replaced and probably fitted with new bushes in the castings. The butterflies should also have been replaced. That is the normal method of reconditioning worn carburetors. If there is any appreciable wear, its worth checking with the suppliers, just in case yours have somehow slipped through the post reconditioning inspection process.
However, before fitting its always best to hold the reconditioned carbs up to the light and check that the butterflies are closing properly and that there is no slop in the main spindles.
All the best and stay safe,
David
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Nick Webster
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Re: Carbs
What a pity that in the last couple of months we seem to have five seperate threads about carbs on the go. All contain useful information but a lot of it is repeated.
Nick
Nick
Hopefully they are altogether in this topic now.
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Keith Clements
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Re: Carbs
I will merge. But it does raise another issue. There is much information on most subjects within JowettTalk but some is in posts and some is in attachments.
The attachments can now be searched using the Archive search which compliments the JowettTalk search.
I hope at some stage to merge these two but a lot of programming is involved.
Then you guys can help consolidate into a readable, instructive library.
The attachments can now be searched using the Archive search which compliments the JowettTalk search.
I hope at some stage to merge these two but a lot of programming is involved.
Then you guys can help consolidate into a readable, instructive library.
skype = keithaclements ;
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Barry20383
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Re: Carbs
The carbs were obtained from Jowett car club spares as recon exchange units.
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Re: Carbs
My comments apply to any reconditioner. If you look at how I reconditioned my carbs and those of a few other members you will see a large amount of patience, tooling, techniques and engineering involved.
One of the most difficult problems is aligning the reaming of the holes for the spindle. This needs to be accurate in three dimension to less than 1 thou. This is not easy to achieve.
See these posts particularly the last.
https://jowett.net/forum/viewtopic.php? ... arb#p19988
https://jowett.net/forum/viewtopic.php?p=20047#p20047
http://jowett.net/forum/viewtopic.php?p ... 05c#p19923
One of the most difficult problems is aligning the reaming of the holes for the spindle. This needs to be accurate in three dimension to less than 1 thou. This is not easy to achieve.
See these posts particularly the last.
https://jowett.net/forum/viewtopic.php? ... arb#p19988
https://jowett.net/forum/viewtopic.php?p=20047#p20047
http://jowett.net/forum/viewtopic.php?p ... 05c#p19923
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David Morris
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Re: Carbs
Hi Keith,
I am very impressed with the skills you have demonstrated with the reconditioning of the carbs. Very instructive and it clearly shows why it costs a lot to have them reconditioned!
There are obviously no short cuts to getting it right and let's hope that all 'reconditioned' carburetors have received the same careful attention.
All the best and stay safe,
David
I am very impressed with the skills you have demonstrated with the reconditioning of the carbs. Very instructive and it clearly shows why it costs a lot to have them reconditioned!
There are obviously no short cuts to getting it right and let's hope that all 'reconditioned' carburetors have received the same careful attention.
All the best and stay safe,
David