Celica 2tb carby issues

[ToyTA22]

I fitted a set of rebuilt 2tb Aisan carbies and manifold, i rebuilt the carbies. Have balanced them and set idle speed and mixtures but have a flat spot just above idle which is about speed in town traffic. It idles fine then on squeezing throtles open it dies unless you get just past that point of opening. It revs no problem above that point. The engine is a 2t bored 1mm over mild cam but with a bit of porting work done.
Can anybody help?

[NME308]

Hi there mate,
It sounds like a nice little engine you have there.
Are you sure there are no air leaks from carb to manifold or manifold to head?
If it were a Holley you played with... I'd have suggested checking the transfer slot was adjusted correctly & ditto for the accelerator pump...
Are the twin carbs you have a factory matched pair originally from a 2tb? Could be that there is either too much or too little pump squirter shot. Could also be the transition from idle to intermediate circuit but I don't know what controls that on an asin carb. Of course with a cam & headwork the fueling requirements will have likely changed.

Is there an idle mixture screw as opposed to just an idle up screw? If so try richening or leaning noting the amount of turns so you can return to your current setting. See if either way makes a positive change & it may give a clue which direction you need to look.

Cheers,
Jason

[ToyTA22]

hi Jason. Thanks for reply. the carbies and manifold are a matched set, by part numbers, from a 1974 TA12 Carina. I found last night, to my neighbours discust, that the idle mixture screws only change engine speed to a point where it idles reasonably smooth. When screwing out further doesn't make much or any difference to engine. My opinion is idle jets are to small and can't compensate for progression. I am used to working with Weber carbies so this is a bit different. The idle jets are a jet and emulsion tube in one piece so obtaining could be interesting.
The engine is in a TA22 celica and I use as daily driver and occasional club motorsport. The club i'm with has a event coming up on 19th October I wanted to compete in, thats why I want to get these sorted.

[NME308]

Unfortunately the lack of commonly available tune up bits like jets and emulsion tubes is what I fear may be an issue.
These babies don't have any form of pump squirter?

Cheers,
Jason

[king-szeitszam]

Sounds like you guys may have found the issue, but just thought i'd put my 2c in anyway- sounds similar to an issue i had running twin carbs on my 2T way back when, ended up that the stock mechanical fuel pump wasn't up to the task of supplying the larger amount of fuel when i went to take off. I ended up installing a low pressure electric pump (5psi) and it was sweet.

[ToyTA22]

Hi king. Electric pump is next thing I am looking at fitting. I have a Carter rotary vane low pressure pump.

Jason. Yes they have a pump and squirter jet in each carby. I have checked those and both work. I probably didn't explain properly, the problem is only on cruising speed on hard acceleration it is fine.

[NME308]

That is where the accelerator pump needs to be spot on then!
Does the squirter react to really small movements in the low opening range of throttle movement? The squirter needs to act instantaniously to cover the momentary drop in air speed when the throttle is opened. Referring back to holley... sorry... The mechanical linkage to the pump squirter needs to be adjusted so there is no play ensuring instant squirt of fuel when throttle is tickled.

If you have already checked this then carry on with whatever you were doing!

Cheers,
Jason

[ToyTA22]

Hi Jason
The Aisan carbies have a vacuum load compensation system to allow for light load changes after that point pump takes over. Set pump to service manual specs, which is basicly as you said.
Regards
Tony