The Cal-look Lounge

Ok guys. Engine started did the break in but now comes the hard part. Jetting my new engine.

Engine is a 1915cc, FK8 with 48 IDA.

Currently the jets are 180 air, 145 main and 60 idle. I first want to synchronize the carbs. I disconnected my linkage and let it idle at about 1300rpm. Problem is after like 10 seconds the engine suddenly starts to rev to 3000/4000 rpm without me doing anything..  ???

EDIT: I have 2 progression holes and 37mm venturis

I also see two other screws on each carbs. I believe these are the CO screws? How can I adjust these? I don't have a fancy CO computer.

What else should I adjust? Float level is ok @ 5.5mm.


Thanks!

Hi Jesse. I'm a newbie too  :D but I'll try to help you anyway!
I have a 1915cc like you, only with an Engle 120 cam.

I'd say the main jets are ok, assuming you have 37mm venturis. On my car I'm using 150 mains and 130 air jets (I know, that's kind of weird, but I wanted to try small air jets like in Porsche 904 engines, and they work well for me, but I never tried the more common 200s, like the tuning manuals suggest to do).
60 idles are good too, I used them first with 115 idle air jets (holders), and car ran good, then I went with 110 and it's a lot smoother. I recommend to try them. I have the stock two progression holes here, if you have the 3rd hole, you should get it running good with a 55 idle, I guess.

I don't really know how to help you with the synchronization, but the other screws you've seen are the mixture screws. They control the amount of air/fuel mixture. To get a steady idle you normally have to set them about 3/4 or 1 turn off bottom. You have to select a mixture screw, rotate it inward until engine speed drops off. Then rotate the mixture screw back out until the engine picks up speed and runs at its best. Then repeat this on each mixture screw.

My engine is very similar to yours, Jesse, and your jetting is very close. Do a quick search here and you will find a TON of interesting and helpful info on jetting and carb syncing. Good luck!

Hell yeah pretty good stuff in here about IDA tuning  ;D

This Advice is even very good for basic:
http://www.aircooled.net/gnrlsite/resource/articles/jetting.htm

Try to turn that idle down to 900-1000rpm at synch and play with the mixture screws. Turn one screw in a bit and wait, than a bit more, wait... at some point the engine will start to rev a bit up and than fall or misfire.Turn the screw back to good rev and than 1/4 more, done.Go to the next...
Most times you have to turn the idle back to 900-1000 as it will be a bit higher after adjusting mixture screws.
Synch is critical for adjusting so make that 100%...

Maybe that rev up problem is caused by:
too much fuel pressure ?
a spitting acceleration pump ?
Linkage incorrect ?

Good Luck!

The cause of this might be your attempt to let it idle at 1300.  At that rpm, you are into the advance of the distributor.  If the engine picks up a bit, it advances more, causing the engine to run higher, causing it to advance, .........
Try setting the idle at 900-1000.

Good point, Bruce. Jesse where is your timing set and what distributor are you using?

I'm using a 123 ignition (dutch product) http://www.123ignition.nl/) it has 16 curves. I set it to 009. Static timed a 9 degrees btdc. I'm now going to buy new sparkplugs and try to start it. Yesterday I checked everything and set timing again etc.

Find out at what rpm it starts to advance.  You have to set your idle speed below that point.

I replaced the spark plugs and the engine instanly fired up. Set the idle to 900 rpm and synced the carbs. I took it out for a short drive around the block. Engine run great but suddenly she started to backfire from all four carbs at once.. She still starts but it backfires like hell. Checked the timing and it is still the same as before it started to backfire.

What else should i check?

two carbs, four throats ;)
good luck!!

sure timing is correct and sparkplug wiring correct? dropped the timing wheel in the case correct? Check this by TDC measure method, than you are sure.  you can never check that enough..

Yes that's all correct Martijn.

hi jesse,

is there no leak between head an manifold or carb and manifold?
check this when your engine is hot and starts to backfire.

what plugs are you runing?

good luck: dirk

I will check that Dirk.

Plugs are NGK BP5es

hi jesse

that is the wrong plug, that's a stock temperature plug (bosch "8")
go for a BP6ES most people run even the NGK "7" in there 044 heads, but 044 run hotter than stock heads.

dirk

Mmm shit :)

I will go and buy them. I have 041 heads.

in my opinion those plugs are too hot for high perf VW application.
But your testing may prove otherwise. I would use BP7ES

1300 rpm idle is too fast. I would try to get the idle to be a rock solid 1000-1100(tops). Welcome to the world of getting IDAs to idle cleanly, pull with no flat spots. I would suspect the 60 idle is right. You should get a nice solid, drone-of-an-idle @ 3/4 turn out on mixture screws, assuming your initial timing is correct.
If car pulls hard off idle but has lean hiccup as it comes into mains, you need smaller (richer) idle air jet hole. If it blubbers and bucks @ steady cruise @ 3000-3700 in 3rd-4th then your idle and main jet are overlapping. A larger air hole probably won't fix that though. And you have to be careful about going smaller on main. Do a full load plug cut and see how plugs look with your main.

see your car in spa ;) ;) ;)
good luck!

dirk

So today another try :). Changes the plugs to BP7ES. And fired her up. Synched the engine and screws are at 1 turn out. Made a small movie :)

Thanks for your help guys

http://www.youtube.com/watch?v=B-QivGh-baI