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Wed Mar 17, 2010 3:17 pm

ok i got a 69 square with dual carbs solexes and it's back firing thru the carbs both of them. at idle it's fine sounds normal but as soon as I hit the gas it backfires thru the carbs. It has a 009 eletric dist. also checked the vavles, they were fine and the balance tube is hooked up and don't seem to be any leaks. There are paper gaskets on the intake manifolds, as for timing, I just double checked it and its fine. HELP been at it on and off for a week.

Wed Mar 17, 2010 5:40 pm

Had a similar problem with mine......were backfiring/popping at idle and on decelleration, the carbs were WAY out of synch, try checking the carbs with a sychnometer and see what's happening and rebalance them ;)

Wed Mar 17, 2010 9:26 pm

also look for intake leaks. spray some carb cleaner around the intake/head mating area. As well as the throttle shafts and any other "suspect" areas. Careful as it is flammable. If you notice a rise in rpm's then you've found the leak.

Thu Mar 18, 2010 1:40 pm

i re-checked the carbs and they were balanced. still have to spray carb cleaner to check for air leaks. after readjusting the carbs still backfireing thru the carbs.I'm ready to pull my hair out. thanks guy for your input keep it coming.

Thu Mar 18, 2010 5:30 pm

I'm going to guess either intake leak... or intake leak via throttle shaft. Stock solex's are known for this. Most machine shops should be able to rebush that for you

Fri Mar 19, 2010 1:20 pm

Had the same thing on my 71 fasty. I found it was a combination of unbalanced carbs and timing was off.

Sat Mar 20, 2010 12:11 pm

I second Buttafuoco's sentiments. I just installed dual carbs myself and found that when the synch was on, but the timing was off, the carbs back fired. Check your timing, what distributor do you have? I've got a 009 dizzy, it's set at 30* full advance. Once the timing was right, the thing runs like a champ. I also had vacuum leaks, so it probably contributed too. Good luck!

Sat Mar 20, 2010 5:17 pm

i just got done changeing all the gaskets from the intake base(had metal gasket) to the base of the carb. checked timing its on the money and stiill it's doing the same thing. i'm thinking maybe the vavales need to be checked or adjusted, hey maybe exhaust leak?. i checked and rechecked the sync of the carbs and looks good i do have a buddy coming over tonite i'm going to have him ckeck the carbs just in case i missed somthing.

Sat Mar 20, 2010 7:33 pm

did you check the carbs themselves? Not just the base gaskets. Where the shaft pivots in the carb body sometimes they wear out and leak there. Also make sure you jets are clear. Pull them out and blow them out with air. No tools, inside jets. Then reinstall them.

Sat Mar 20, 2010 7:42 pm

Your timing is off. If you set it to stock specs with the 009 that's your problem. get a tachometer on there and set it at 30degrees before top dead center at 3000 RPM.

Sat Mar 20, 2010 9:02 pm

YES the timing was the problem i was setting it to stock, so we kept playing with it and it sounds alot better now not getting the backfire. thanks guys you all helped me out.

Sun Mar 21, 2010 5:54 am

Ok, dumb question, I only know how to check timing static with a test light.

How would you test with a timing gun and know it is at 30*? Are there markings on the fan to know when you are at 30*? If so, I need to get a good timing light.

Just curious....

Thanks!

Sun Mar 21, 2010 7:08 am

no the fan does not have marks for 30* advance. You need to buy a good timing light that you can adjust the advance. Then you set the timing light to 30* and it will strobe when the fan is at 0*. If you are buying a timing light I recommend also getting one that has a tach in it. Sears has them for around $50-$150.

Heres the one I have, which can also be used as a flashlight if needed.

http://www.sears.com/shc/s/p_10153_12605_00914066000P?keyword=craftsman+timing+light

Sun Mar 21, 2010 8:19 am

50mm to the right is 30 degrees.

Mon Mar 22, 2010 4:51 am

Once I go EFI, which should start the summer, static won't work for me anymore. I think I know the timing light of which you speak.

Russ, thanks for info. I assume you just roll the crank +50mm and then set the dizzy to fire at that mark?

Mon Mar 22, 2010 10:25 am

That will not work for static timing.
That will mean you are 30* initial advance.
Do not know how you would static time with an EFI system.
I do know that you can static time a Pertronics, with a test light. BTDT.

Sat Mar 27, 2010 6:27 am

Static is going to work for me until I go EFI. With my carbs I am 100% stock, so static is fine.

I will use a timing light for my efi, once that project starts, but I have a motor to rebuild and many other repair/modifications to do before that project starts......

Thanks for the info Russ.