Technical weber 26 carb rebuild / tuning

[Paul fairall]

Yes I might be interested in doing that. Let me get back to you tomorrow.

 

[Paul fairall]

Maybe not of much interest to others here as its not a fiat 500 but my ford sidevalve has a Weber 26 IMB. With the standard zenith carb it struggled up hills at 20mph. Now it gets up hills at 40mph. Proving my thoughts that the engine struggles to breath. Thinking a 28 might be better with standard jets rather than the 26 with larger jets.

 

[Toshi 975]

Simple answer is nothing, the IMB10 was fitted to the 500L and the IMB6 to the 500F. Same fitting and specification.

 

[Paul fairall]

Had the weber 26 IMB 10 on my ford sidevalve for some time now and pleased with the performance of it such that it is. But I have a problem starting from cold. Engine fires briefly and dies several times before eventually struggling into life, I have to leave it until it's running a while before opening the throttle or it dies. Turning the idle mixture screw in or out makes no difference to how it runs and may have some bearing on why it struggles to fire up. I'm going to ultrasonically clean the carb again and blow it out with air but if anyone has any suggestions I would appreciate them.

 

[the hobbler]

The IMB series of carbs do not have a 'choke', but a 'fuel enrichment device'. The problem could be as simple as what is ample enrichment for a 2 cylinder 500cc engine, is not enough for a 4 cylinder 1172cc engine. The fact that you have to let the engine warm up before you can drive away would seem to support this thought. Adjustment of the idle-mixture screw having no effect on this problem would be another pointer to the fact that cold-start enrichment is not enough. Fitment of the bigger 28IMB MAY improve performance, but the cold-start-warm-up problem will, I suspect, still exist.

 

[Paul fairall]

Appreciate your input. As I was told the 500 is a twin and the ford is a four cylinder and both engines only fire one cylinder at a time. Ok the ford is 293cc per cylinder and the 500 is 249cc I guess so 20% bigger capacity. I did consider the 28 but I adapted the throttle linkage with a part from a solex that connects to the rod operated throttle of the ford and this rotates in front of the idle mixture screw, yes the one that doesn't seem to work. The 28 carbs mixture screw sticks too far and would foul on my throttle linkage.

 

[Paul fairall]

May not be of much interest here unless you have a bigger engine or have tuned it. I have a ford sidevalve 1172 with 26 IMB 10, with 130 main jet as the each cylinder is 293cc and the fiat 500 is 249cc. Runs great and gets up hills at 40mph whereas with the standard zenith carb it would struggle at 20mph. But as the weather has got colder it's struggled to fire up and stay running and has taken countless turns to get it to stay running. Starter jet is 90F5 so I searched for a supplier with other size starter jets. I found one in Czech Republic and another in Italy both on eBay. I ordered a 100F5 and 105F5. Fitted the 100F5 and it fired more easily but needed several cranks so fitted the 105F5 and it fires right up and runs great.

 

[Bigvtwin996]

I wish there was someone who had nothing better to do than collate all this info....
It is bound to happen in the future that someone has a problem and the solution is lost in the depths of 00s of threads....

 

[Paul fairall]

I wish there was someone who had nothing better to do than collate all this info....
It is bound to happen in the future that someone has a problem and the solution is lost in the depths of 00s of threads....

it seems the companies selling carbs and parts like eurocarb only go by the standard spec sheets, I guess that's the only thing they can do. As for collating info, that's fine if that info is correct. What I'm finding may not be of use to someone with a fiat 500 and also wrong info can make things more difficult to get a good result. All I can say is the info I gave been given regarding fitting a 26 IMB 10 to a ford sidevalve 1172cc has given a good result and my own choice of starter jet has also worked.

 

[Emro99]

Hoping someone can help.

My car has a 26 Imb 6 fitted but the car refuses to run without the choke being out. When warm, choke in, car dies. Assume it’s something simp,e with adjustments but damned if I can get things any better. There’s so little that can go wrong but seems beyond me.

Any ideas?

I also have a 26 IMB 4 but can’t see any difference between the two. Worth swapping?

 

[Toshi 975]

Carbs are completely interchangeable. You may have a blocked slow running jet or poorly adjusted mixture screw. That is assuming the valve clearances and ignition timing are ok.