General Weber 26/28 IMB

[Veloman518]

The emulsion tube DOES come out BUT BEWARE; behind the little brass cap that covers it is a spring, which if you are not aware of, will pop out when you remove the cap and dissapear into the darkest and most remote part of your workshop--and they are NOT a purchasable part! How do I know? despite clearing out my old garage when we moved to Wales, I never found the spring out of one of my IMB carbs! (luckily, it was one I only used for spares). If you would like me to, I will look in my workshop tomorrow and see if i still have that carb---if i have, you are welcome to the butterfly shaft---what size IBM carb do you have---my spare is a '28'.

28 IMB and if you have the butterfly shaft and screws for that you will be my friend for life.

 

[the hobbler]

Good morning "Veloman518". Well, aren't you the lucky one! Although i don't have the carb, I obviously stripped it before i did something with the body of the carb because in my "Weber IMB" box there is a complete butterfly-shaft; butterfly, screws, shaft, end spacer, spring and nut. If you would like to contact me direct ( [email protected] ) with your home address, i will put it all into the post to you. I hope that this gets you out of trouble.

 

[Toshi 975]

The emulsion tube DOES come out BUT BEWARE; behind the little brass cap that covers it is a spring, which if you are not aware of, will pop out when you remove the cap and dissapear into the darkest and most remote part of your workshop--and they are NOT a purchasable

Tom me old mate I think that you are getting confused with the choke (fuel enrichment) mechanism. The emulsion tube is removable but it sits under the air correction jet. It can be difficult to remove but I generally give it a squirt of WD40 then I have a screwdriver that is pretty much a perfect fit down the centre so give it a good waggle and it generally comes out.

 

[Veloman518]

Tom me old mate I think that you are getting confused with the choke (fuel enrichment) mechanism. The emulsion tube is removable but it sits under the air correction jet. It can be difficult to remove but I generally give it a squirt of WD40 then I have a screwdriver that is pretty much a perfect fit down the centre so give it a good waggle and it generally comes out.

Thanks Toshi, I broke down and got an ultrasonic cleaner (I have a bunch of old cars and bikes so it will get used). It was really gummed up so let some carb cleaner sit in there then a few cycles in the ultrasonic and it finally dropped out. It was pretty nasty.

 

[the hobbler]

Woops!! In my defence, it was late at night that I posted the message and about 4 years since I last stripped a IMB. However, one still needs to be careful as that particular spring is not listed in ANY parts list. I bow to your chastisement David.

 

[Veloman518]

Should I try to dress these ridges out or let them be? Last hole at the bottom is exposed when the butterfly is closed. They aren't as deep as they look. Can just feel them with my fingernail.

 

[Veloman518]

Also I appear to have a license built Polish Weber

 

[Veloman518]

Does anyone know if the base mounting plate (the Bakelite piece) really matter between carb types? My 28imb is mounted on a 26imb mount to the engine. It all fits but I don’t know if it’s possible causing issues with correct mating surface and air/fuel flow.

 

[Salv77]

I have a 500R with the 595 engine I did have a 28imb3 and was running fine but float had split so bought a 28imb5 with 0.50 idle and 115 main jet, blocked the fuel return as my previous carb, but is running rough? No matter how much I adjust mixture/idle I can get it in sync? Any ideas/tips if this is the correct setup for me.

 

[the hobbler]

Have you checked the jets on the '5' vis-a-vie the '3'? If they are different, it might be worth while putting the jets from the '3'into the '5', or even, just putting the float from the '5' into the '3' and putting the '3' back onto the engine. On the 126 cars with the 28imb carb, the fuel return is utilised---is it in the 500R? If it is, I would suggest returning to that system, which also helps with some 'hot-start'problems as the fuel is constantly flowing, and therefore self-cooling.

 

[the hobbler]

answer to your query Joe regarding the bakelite spacer---(a) it IS required as it helps insulate the carburettor from the engine heat and (b) it is wise to fit the correct spacer as I think that the orifice (posh word for 'measured hole') in the spacer is compatible with the appropriate carb

 

[Salv77]

Have you checked the jets on the '5' vis-a-vie the '3'? If they are different, it might be worth while putting the jets from the '3'into the '5', or even, just putting the float from the '5' into the '3' and putting the '3' back onto the engine. On the 126 cars with the 28imb carb, the fuel return is utilised---is it in the 500R? If it is, I would suggest returning to that system, which also helps with some 'hot-start'problems as the fuel is constantly flowing, and therefore self-cooling.

It’s is a 500R and previous 28imb 3 carb did have fuel return blocked off so have done the same on new 28imb5

Will check the jet no.’s and compare. The mixture on my new carby is recessed whereas old one has a spring on the adjustment screw.

Just wondering if anyone out there has a 28imb and what size jets they are using to get good performance?

Thanks

 

[the hobbler]

The 652cc '126' Used a 28IMB 5/250 as the standard carb. The jet sizes were:--Main:---------------------115
slow running--------------50
slow running air bleed---140
Needle-valve-------------1.25mm
Float level----------------7.0mm +/- 0.25mm gasket surface to float.

The problem is, in the '595' 126 workshop manualall the jet sizes are given in mm, which is difficult to corrilate with the 'number' jets. My suggested first move wold be to put the good float from your '5' into the '3' and see how that goes, because as you mentioned,the car went fine untill the float failed. I would also suggest that you get a new float--they aren't expensive and they cannot be repaired.

 

[fiat500]

I have a 500R with the 595 engine I did have a 28imb3 and was running fine but float had split so bought a 28imb5 with 0.50 idle and 115 main jet, blocked the fuel return as my previous carb, but is running rough? No matter how much I adjust mixture/idle I can get it in sync? Any ideas/tips if this is the correct setup for me.

I had some problems on a 594 with a 28IMB...not sure of the number. When I looked closely at the slow-running jet it had become slightly compressed.It was a 0.45mm. I intend to get hold of the correct replacement, but for now it's on a 0.5. I was able to get the mixture spot on, but I used a Colortune. You probably need to ignore the original advice about the mixture screw being around 1.5 turns out. Try to adjust the mixture with the engine as close to stalling speed as possible.

 

[Toshi 975]

Originally the 500R cars were fitted with a 24IMB carb as opposed to the newly launched Fiat 126 that had the 28IMB 3. Fiat wanted to detune the 594 engine compared to the 126 on the 500R to give the 126 an edge as the 500 was coming to the end of the production. A simple tuning mod for the 500R was to fit the 126 carb so in theory you should be able to run a normally jetted 28IMB. Hairline cracks in the floats is a common one leading to the engine flooding. It has to do with the deep drawn brass and ageing. Can be hard to spot but new floats are easy to get and cheap to buy.

 

[Salv77]

All sorted with co2 tune purrs like a lion ? now thanks for all advice