backfire on crossflow

[smosar]

When I accelerate there is a stutter as the engine picks up. On decelerating the engine backfires. When I stop there is a loud bang from the exhaust

The engine is a 1700 crossflow with 234 cam and twin 40"s.

There doesnt appear to be any leak on the exhaust side. Do you think air might be getting in at the carb / manifold joint. If so Ill change the gaskets nuts and rubbers. Alternatively does it just need tuning or carbs out of balance

Any thoughts appreciated

[Mid life crisis]

Sounds a bit like my crossflow. feed in the loud pedal progressively and see if it picks up normally. Then when changing down, do it at the highest revs that you feel comfortable with. Then try it again in an enclosed village enviroment.

The point of this test is to see how many car alarms you can set off on one street. my record is eleven.  

Quite normal for an xflow.

But probably running a bit rich.

           

[ray5wood]

     

QUOTE

The point of this test is to see how many car alarms you can set off on one street. my record is eleven.  

 

[Mid life crisis]

Sorry smosar! thought someone would have been along with a more sensible reply by now.

The way you describe your xflow running is very similar to my car when I first acquired it.  I eventually arranged a rolling road session after numerous unsuccessful home made fixes.

Jetting in the 40's was identified as the main culprit "overfuelling". which was rectified by re jetting the carbs, after which all seemed to be good. The car pulled cleanly from 1200 RPM right up to the rev limiter. but the backfire has always been present. However this may be indicative of the very small Raven Racing silencer I run. At best it gives a reading of 103 dba.

I haven't really driven the car much over the last 18 months, but have noticed on the road a slight hesitation when pressing the loud pedal flat, up to about 2500 rpm, after which it pulls cleanly. However if I apply progressive pressure to the pedal the car pulls cleanly from 1000rpm.

I have made no changes to the car in the interim so can only conclude it may  be the carbs . The only two other factors during my ownership of the car that have caused performance problems have been a faulty fuel pump and a perished fuel pipe exiting the tank which was allowing air into the fuel system under load.

Best of luck in sorting it.

Steve.

[RedditchJay]

sound like unspent fuel to me or slighty off balance butterflies

[Nomexnomad]

Over fuelling for sure, whats causing it is the problem. Main culprits are incorrect jetting as said above, but also out of balance carbs will cause it also, a good rolling road should sort it