backfire on rebuilt 225 engine

Hi,
I'm having trouble getting my newly rebuilt engine to run correctly. Everything on it is new, with the exception of the carb (it had no carb when I got it.) The engine is a 225 casting #B1358435 which would mean it came out of a 1963-65 Buick according to the info that was in the tech section. From the info I've been able to obtain, the engines original carb would have been a Rochester B, BC, or BV. I had a extra Rochester B from a 66 GMC truck that I have rebuilt and installed (one barrel/one barrel manifold) The truck had a 250 straight 6.

When starting it had a lot of sharp backfiring. Adjusting the dist. doesn't make any difference. It seems like it is getting to much gas.

Can anyone verify that the Rochester B I currently have on it is an acceptable carb for this engine. If so, I'll know something is wrong with the carb. If not, would anyone happen to know what model would work?

Thanks in advance for the help. I'm really in need of some expert advice.

 

I would double check the firing order and inspect the cap and rotor, even if they are new.

 

when you say its back firing, thru the carb, or out the tailpipe??? if it is back thru the carb it could be too lean...... rebuilt engine.......... are you certain that the cam timing is spot on, if you were into the engine that deep??

 

Thanks for the responses.
I will go ahead and replace the rotor and cap. I have already replaced the condenser, coil, and ballast resistor.
I think it's and odd fire distributer. It is new from Napa. part #48-1611 I looked up the ticket and it has "1968 Kaiser Corp. CJ5 3.7L 225 CID V6" listed as the vehicle. It looked identical to the old one. Does this seem OK?

I did totally rebuild this engine and also did a total rewiring. I tried to be very very sure that the dots were lined up between the cam gear and the crank gear, but I guess I could have screwed up. At least I knew how important it was at the time. As a last resort, I'll take off the cover and have a look.

It was backfiring mainly out the exhaust, but I did get an occasional one through the carb. I guess I was thinking carb issue because at one point it seemed to be running "correctly" but with short sharp backfires out the exhaust, like extra fuel was getting through the engine.

I have the same carb. on my old truck, and I know that runs fine. I guess I could put that carb. on to at least remove one variable.

Thanks

 

backfiring out the exaust, sounds like a timing issue, or like patrick said misplaced plug wire, i had a 225 years ago that ran fine, but it would backfire on decelleration, got the law called on me once, they thought i was shooting a gun in town

 

I have to ditto kaiser_willys remark about the backfire on deceleration. Mine does the same thing: and yes - it's like gun fire. Even if I let the engine wind down between shifts, I'll get a loud pop.
I do have an exhaust leak at one manifold to pipe connection, and it should be less of a problem once I get new exhaust. Apparently, the leak allows enough air (oxygen) into the exhaust pipe to allow combustion of any unburned fuel, and causes the backfire.

 

Yes, I've checked the plug wires about a dozen times. I've even checked them under supervision. Engine @ TDC #1, distributor installed with rotor facing "forward" towards the window and at #1 location on cap. (cap is numbered) Wired to cylinders as listed in my manual. Drivers side 1 3 5 Passenger side 2 4 6. Does this sound correct so far?

Thanks for narrowing down the problem to timing.

I'll let you know if the new cap and rotor help or not when I get them tomorrow.

Thanks for all the assistance.

PS. This side had helped me so much I can't tell you. I gained lots of knowledge in the old archives.

 

Thanks Patrick,
Knowing what you've done right, helps one determine what you've done wrong.

 

What is your vacuum gauge showing while at idle and also about 1500 rpm? Is gauge steady - is it jumping around?

 

Well,
I'm still waiting on the new cap and rotor since I had to special order them. Won't get until at least Wednesday.

I haven't had a vacuum gauge attached as of yet. I do have one that I got for another project. Thanks for the tip. I'll try to attach prior to restarting.

 

do you have a dwell meter? points out of adjustment will cause these symptoms as well

 

have you figured out the problem yet?

 

Have you adjusted your points gap and dwell?

 

I do not know this engine, but many of the old engines had distributors that had shafts fitting into the oil pump. If the oil pump was installed with its shaft 180 out, then number one cylinder would not be where you thought it would be. You still could make most of them work by selecting the positon for number one based on the tdc position of the number engine cylinder.

 

I think w3srl might be on to something, would have been my 1 st guess.
Then again, my FLPS showed 3 dist. caps that would fit my commando (delco).
The one not in stock was the one I needed.