QuestionQUESTION: My Marauder has cobra slip-ons and valves were recently adjusted. Pilot
screw is set at 2.5 turns out. Bike starts and idles perfectly. Cruising around
20-25mph and decel both experience popping in the exhaust. The PAIR valve
has been disabled and re-enabled and that didn't fix the issue. I've checked
the exhaust header bolts to ensure they're tight and they are.
What recommendations do you have for me to help remedy this issue? When I
roll on the throttle, the response is very good. Do I need to richen the mixture
a little more? Are the carbs out of sync? I'm not familiar with the carb setup
on this bike, as it's new to me - two days new. Any exact directions or
diagrams you can provide would be ENORMOUSLY appreciated.
Much thanks,
Mike
ANSWER: Mike,
This is quite common with aftermarket exhaust systems.
They are not baffled as well and so have less backpressure.
This leans out your air/fuel mixture.
Always use new header gaskets if possible, tiny
leaks can cause backfires. If you have a cigarette
handy, hold it near the exhaust flange and see if it
sucks the smoke in, hence a leak. You may need to
plug the PAIR eventually. The needles in the carbs
can be raised to richen the mid-range fuel.
The main jets need to be replaced for high-speed
and overall fuel increase. You can try turning the
pilot screw out a bit more. Also if your intake
valve clearance is tight, this would not help
as air may sneak in there. Don't be surprised if
it is difficult to eliminate the backfiring completely,
better men than me have tried and failed. :)
---------- FOLLOW-UP ----------
QUESTION: Thanks very much for your advice. 'Nother quick question. Not being at all familiar with cycle carbs, what kind of increments would you recommend I use to turn out the mixture screws? As mentioned earlier, they're 2.5 turns out, which is the recommended amount for the Cobra slip-ons, provided that the jet kit is installed. I've not yet determined that, though.
ANSWER: Mike,
I think a max of 3.5 or so on the pilot would be worth a try, but as you mentioned it depends on the other jets etc.
You said the idle was ok but anything might help
to richen the mix to cut down on backfiring.
Premium gas burns slower, you could try different brands
and octanes as an experiment.
---------- FOLLOW-UP ----------
QUESTION: I'm at three turns now, and the needle is clipped in the recommended position.
There are two shims under the e-clip though, and I'm without a manual of any
sorts for this bike. Would you agree that it might be a good idea to try removing
one shim from each needle?
AnswerMike,
When the needle goes up the fuel mix gets richer,
needle down makes it leaner.
Usually this means lowering the clip so the needle
is raised for enrichment.
Just look at the needle and visualize if you
want richer or leaner and move the shims/clip
accordingly. If you want to richen the mix alot, you will have to up the main jet size though.
One note, as an idea on reducing backfire, have you looked
into getting torque cones? Check with "Cobra" to see
if they offer anything like that.
