Page 1 of 1
bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 7:05 pm
by lelocp
So i went to start my bike today and for some reason it wont start. I have spark and gas. After tweaking with the carbs the bike started but was only running on one cylinder. So i decided to check if the other carb was doing its job. I began adjusting the idle control screw and the idle begin to rise on the suspected cylinder that was not firing. Im beginning to think that the compression is low. but how can the bike all of a sudden begin to run poorly? ive taken the bike out several days ago and it was running great. im really stumped.
Re: bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 7:13 pm
by Garnet
Are the chokes/enrichers fully activated by the choke cables?
Water in the float bowls?
Points closing up? (Only the perfectly adjusted carb will fire)
Re: bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 7:48 pm
by lelocp
points are good, choke is activating, no water in the bowls. The right cylinder that doesnt fire has a loud backfire
Re: bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 8:48 pm
by Garnet
Swap plugs left to right. Then the plug wires.
Blow out all the jets and air passages on the RH carb.
Long shot: Has one of the valve adjusters come loose not letting a valve open? It would make an awfull racket.
Re: bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 9:33 pm
by lelocp
i swapped the plugs and there was no luck.
Re: bmw 75/5 runs poorly
Posted: Sat Sep 29, 2012 10:53 pm
by Deleted User 62
nevermind, it was just the pain killers talking....
Re: bmw 75/5 runs poorly
Posted: Sun Sep 30, 2012 10:40 am
by SteveD
Carb bowls off.
Inspect for water.
Blow out the little jet in the corner. Run a bit of fishing line thru it.
Inspect the gaskets. If they're very rounded at the holes, replace 'em. Too much air can be entrained when cold making starting difficult.
Re: bmw 75/5 runs poorly
Posted: Sun Sep 30, 2012 5:37 pm
by Major Softie
After making sure there is spark and fuel getting to both sides:
1. Switch plug wires from one side to other
If no change:
2. Switch plugs
If no change:
3. Pull the valve cover and make sure the valves are adjusted and operating correctly on the bad cylinder.
If no change:
4. Switch carbs from one side to the other.
If no change:
5. Do compression check (although if one side isn't getting warm it will be difficult to get a sure reading).
I've tried to list this in order of time it takes to test. You could switch the order of 3 and 4 as they are very close in time requirement.
Re: bmw 75/5 runs poorly
Posted: Sun Sep 30, 2012 5:41 pm
by lelocp
i found out that the spark plug was not seating correctly, so the compression was low. Now this head was previously helicoiled and it appears the helicoil is coming out. I know they sell big serts for damaged helicoil jobs. I find that a used head with good threads is cheapier then the kit which costs over 300 dollars. Can i use heads from other airheads that will work.