I have a carb'ed teener that is having some problems. Every since I bought the car I have had problems with the carbs (40mm Dellortos). A friend of mine let me borrow his until I get my fixed (his run great on my car). Well it has been a while and I want to get them back to him. So I am looking for words of wisdom.

I am getting a lot of carb backfiring so I rebuilt the carbs and had exactly the same problem. I found a couple of places they were sucking air and replaced the O-rings with another set and that fixed those leaks but I am still backfiring. I assume that it is still sucking air (need to test it again) or an air passage is blocked. Tonight I will tear them down again and let them soak for a day or two and then blow them out really well. I thought I had cleaned them well enough but you ever know. I also think that the jets may need to be replaced with different sizes (I am going to start out with the same size jets my friend has since I know they work with this engine). I don't have the sizes with me here at work. What size jets do most people use? From what I know the cam is original so it was designed for FI. This winter I will replace the cam and most likely rebuilt the engine.

TIA

QUOTE (mikelsr @ Aug 29 2005, 01:59 PM)

A friend of mine let me borrow his until I get my fixed (his run great on my car).

don't know a thing about Dellortos but i'll bump this thread anyways ...

maybe your friend is *OK* with a carb swap? keep his and give him yours?
Andy

I'm a big Dellorto fan and have run them for years on bugs, so maybe I can help. First things first, be sure and get a full rebuild kit and do it right. Second, buy the CB Performance "Dellorto Superformance" book. Read it many, many times until you understand it. Finally, main jets should be roughly 4.0b x Venturi size (so a 40mm vent would get a 160 main). Idle jets should be 60's with about 3-3.5 turns out on the idle mixture screw.

Rebuilding and tuning any carb is a science, if you have any doubts you can do it contact ACE (Aircooled Engineering). He can rebuild and test your Dells for you for a respectable price. Art Tharen is his name and they are in Salt Lake, UT I think...

-Aaron

Popping thru the carbs at idle = lean. Could be plugged idle jet, too small idle jet, mixture control screw not adjusted properly..(adjusting inward leaner...outward richer)

40 mm Dellortos come with 34mm venturis,140 mains, 60 idles, and 180 airs.

Carbs suck period!
wish i had a pair

Thanks for the info. A long time ago I rebuilt carbs a lot but that was over twenty years ago. I am giving them a real good soaking and cleaning and I hope to have them back together this weekend. I'm going to transfer the jets from the working pair to mine and then more likely have to order some new yets.

I have purchased the book and I have read it and learned some stuff. I also bought the complete rebuild kit and the CB update kit for the DRLA.

My carbs have either 50 or 55 for idle. When I talked to CB they suggested I get 160 mains, 60 idle for it and I would have to go see what the airs were.

My friend has some weber's on his and was having some problems with them and that is why he wanted his carbs back. I hope to have them to him this weekend. If I have to I will send these off and get them rebuilt.

Again thanks for your help.

Mike

I dunno Mikelsr. I think 160 mains may be a bit too big for those carbs. I'm running 45mm Dells with 38mm vents, 180 airs, 160 mains and 70 idles on 1911cc engine with Web 86 cam and 8.6/1 comp. I also have the CB update kit on them. It idles and runs super smooth.
Make sure you syncronize them too, and your linkage is adjusted correctly and tight.
Dellortos are great carbs once you get them tuned.

What size venturi is in the carb body? What carbs are these (40,45,48,48 Tri-jet)?

-Aaron

Had my Dells for 10 years, love em

PugBug hit it on the nose...syncro - ization and throttle linkage.
When it pops thru the carb is a lean condition, if your carbs are not synked or linkages are not tuned causing one side to be leaner/later, on a accelleration/off idle.

When I first put them on, it took a while to figure out the sync. These carbs are nutorious for "whistle" under accelleration, not a vacume leak. If anything check your intake gaskets, I have had problems with jobber gaskets.

A carb overhaul is never lost, just good maintenance !
I will be doin my baby Dells shortly, gonna check out that update kit from CB

Keep us informed !
later

turning in each of the idle/air mixture screws, one at a time while noting the number of turns, will indicate if you have a pluged idle jet or idle jet circuit issue. if turning a screw in produces little or no effect, it indicates you have a problem on that particular one. you should sense a noticable stumble of the engine or popping in the exhaust note. after the rebuild, it's best to go through the initial setup proceedure. i'm more familiar with webers, do dels have the same type of air bypass screws? if so, double check that they are at a common setting. 60 idles "sound" a little "fat", but i see no mention of your engine's particulars.

k

Yup.....They sure do whistle!

Ok, here is what came on the carbs:

idle 55
main 180
air 140

Recommended by CB performance
idle 60
main 160
air 160

The recommended is what is working on my teener now. BTW it is a bone stock 2.0L engine with carbs. A winter project is to give it a new cam (and maybe some more).

I have the 1st carb back together and the second one soaked and cleaned. I will reassemble it on Friday (I have a welding class on Thursday nights) and test them on Saturday or Sunday. I think I am going to the opening ILLINI football game.

Once I get the carbs so there isn't much backfire I will sync them (don't want to burn up my sync meter).

Thanks for all your input.