New points,timing ,valves and cam chain

[Scrambled]

A shop up the street from me has a stock '78 E in for repairs . The mechanic ( a Harley guy, but will work on anything ) has tuned the thing to spec but it is backfiring on the left side . He thinks it may be a carb problem although they look clean , bike starts right up . He wants to buy a new set of carbs for it, or a decent set of used ones ( quick fix , I told him he is better off trying to work with what he has ) . Any ideas on why the thing is backfiring on left side ?

 

[Scrambled]

Also, just to narrow it down a bit , the vacum lines are good, exhaust not leaking ( stock type double wall pipes , no cross over with mufflers off a later special ) stock air box , but I did notice that he has two different petcocks , not sure if that matters .

 

[deadchef]

backfiring on the left hand side and he wants to buy a new set of carbs?? well at least you figured out who NOT to take your bike to!

i'd go back through the specs and double check everything. obviously something is amiss.

sorry, not much else to offer.

 

[Scrambled]

LOL , he has a busy shop, I think he just want's a quick fix to get rid of a pain in the ass customer that doesn't want to spend the money it takes to properly restore a 36 year old bike . I know he did a proper tune up and has re-checked everything .

 

[deadchef]

well if he's certain the backfiring is just out the left hand side, i would start checking the points, timing, float level and o-rings in the left carb...

 

[Scrambled]

Sounds like a good place to start . He did put a brand new set of points on , ( I am trying to talk him into a Pamco set up ) , I have a brand new set of stock coils, points and condenser that I am going to give him ( a good will gesture ) , but I think he is going to have to get into the carbs too . Seems like it is the customer that want's a new set ( they are always right ,right ? )

 

[weaselbeak]

I'd get my bike outa there. Is it backfiring or just popping from being lean? Some "experienced" people don't face up the points correctly and get lousy performance from them. Could be anything, even a coil, but to suggest new carbs already is just a haphazard guess.

 

[Scrambled]

Not my bike, shop up the street from me . I know , the new carbs sounds like a shot in the dark to me too , but I think it is the customer that wan'ts them and the mechanic just wan'ts rid of the customer . I am going to try to talk some sense into the newbie xs owner if I see him .

 

[5twins]

New carbs, especially a high performance set like VMs, would most likely present a whole host of new tuning problems, probably much more than a little backfiring from one cylinder.

You say the carbs look clean but that don't mean nuthin'. The pilot circuit may be obstructed in that left carb. Also, although the mix screw setting spec is 2.25 turns out for this carb set, they usually like more, closer to 2.5 or 2 5/8 turns. You'll get popping if they're set too lean.

 

[Scrambled]

I talked to the mechanic yesterday , seems like there were some miscommunication between the front of the shop , the customer and the mechanic that was actually working on the bike . I lent the guy with the greasy fingers my service manual and showed him the carb guide on here , and he agrees that he is better off working with the stock carbs that are on the bike ( they do seem to be in good shape ) now he knows where to get parts for them and has the guide .