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Running on one. (cylinder that is)

  • Thread starter Thread starter n1elkyfan
  • Start date Start date
N

n1elkyfan

Guest
I have a 1979 GS750L that I have been working on for the last two months. I have been having a problem that when I start it for the first after it has been sitting for a while. It will idle for ok, but if I shut it down then try and start it back up after sitting for about a minute It will be hard to start and will only run on one cylinder and eventually dies. I have adjusted the points it ran better but after I shut it down It went back to running on one cylinder. I check that spark and on cylinders 2,3,4. It was really weak but on cylinder one it was stronger. I pulled the plugs when it first started acting up. The 1,4 plug were darkened from firing but the 2,3 plugs looked new. Also the 2,3,4 plug were wet. I swap the 1,4 plug wires and it didn't make a diffrence it was still only running on the number one cylinder. I just have run out of Ideas on what could be wrong and could use any help.
 
Your mixture is too rich and your spark is too weak. When you first start the bike (after it not having been run for a while) the plugs are nice and dry and the carb bowls are not overly full (some fuel has evaporated from sitting), so it will run OK initially. The longer it runs, the wetter those rich cylinders/plugs get. The weak spark makes things even worse. Eventually those cylinders cut out from over-richness.
Switching the wires may not prove anything because the good carb/cylinder may be just good enough that even a weak spark won't make it cut out eventually.
This scenario is commonly due to one or more of the following:
1. Imperfectly sealing float needle valves
2. Leaking floats
3. Wrong float height
4. Low compression (typically due to insufiicient valve clearance - but can be bad rings, head gasket leak, etc.)
5. Pook spark due to bad plug wires/caps or due to failing ignitor/coil/pulse generator (these CAN degrade in a gradual manner)

NOTE: I have had ALL of the above problems on one or more of the five non-running bikes I've restored to daily riders (I've been riding for 19 years).

The steps to verify these are discussed to death on this forum - do a search.
Using this forum will save you tons of time and money.
 
I'm going to try and fix the weak spark by replacing my plug wires. I think my coils are good I checked the resistance on the primry side it it was 5 ohms.

I have been using the search alot I just haven't been able to find anything that has helped me.

There have been a couple things I have been wondering. For tunning the carbs I seen people say things like turn it out 1 1/2 turn out is this turn out from when it bottems out. I was also wondering if you could use auto coil on a bike. I was thinking of something like this http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_747653_-1_10681 or this http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_752720_-1_10681
I figured this could be a cheaper performance coil then even a factory replacement coil. The stock replacement on bikebandit.com is 92.64 for one and I haven't found any aftermarket coils yet.
 
What about the first 4 items in the list I gave you? Especially the fourth (have you checked compression?).
If you can't find the posts that speak about how to verify the items in that list I gave you then you need someone to walk you through the search feature - it is very much like the search feature on countless forums, so find someone with experience in searching forums.
 
I have checked the first three I haven't checked the compression yet because I don't have a compression tester. I'm leaning toward the spark being the problem because it is very week, almost none, that and the fact they look original to the bike. I know how to use the search my problem has been that most of the information I have for found is for 80 and newer bike that have the CV carbs and electronic ignition. I have VM carbs and points.
 
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