Can't figure this out.

Hi folks.

I have an 81 xj650 that ran very well all summer. Lately I just can't get it to start. I pulled the plugs and they are very black. I sand papered them very well as they have lots of life left and are sparking on a test very well.
I ran some carb medic through it last week on a long ride (after much difficulty starting it) and put some premium in the tank today. But no start again.
Any thoughts I would really appreciate.

Thanks

Kurt

 

How long has it been since you pulled the carbs to clean and sync? With it running rich there is something out of adjustment in the carbs. Stuck floats or sticking slides comes to mind first. Check your oil and see if there is a gas smell, over flowing floats will fill up your crankcase with gas.
Start with a new set of plugs and see if it starts, even though you cleaned them the carbon left down inside will affect the spark.
While they are out go ahead and check the valve adjustments.

 

Engine needs three things to run and they are: air, fuel and spark.

I'm not up on the electronic ignition but it sounds like you have spark whether it it is at the right time or not, I don't know. It sounds like you have fuel. Have you tried pulling the air cleaner out? Have you tried dropping a little bit of fuel down the plug holes before giving it a kick?

 

Benchpress- - can you post up your compression numbers, and the results of your float/clear tube check??
Are you twisting the throttle as you try to start??
Did you check your battery level and charge??
(all good advise above BTW)

Can you start your bike (on a battery charger) by dropping a small gas soaked rag bit into the air box?? (safety cautions noted)

I'm thinking you have weak battery/plugged jets.

 

Air cleaner was pulled and a new was put in.
Battery is brand new.
She starts with a little woft of starter fluid misted by the intake but only runs for a second.
Tried the gas down the plug housings and same thing.

Will try new plugs for sure.

Not sure how to perfom a float check or carb synch. Any advice?

 

Search the forums for " carb sync" and "float level". There are many how to articles for each. Most likley your problem is carb related.

 

?Could be an petcock problem. Set to "prime" and see if it starts. But don't leave it on prime. If your carbs are messed up you will fuel in the crankcase.

MN

 

engines need 4 things to start, #4 being COMPRESSION.

if it starts with ether, it should have no problem starting with the enrichment circuit open ("choke"). ether also will combust with much lower compression (heat) than gasoline, so if you have bad rings or tight/bad valves, that will cause your symptoms as well, including the black plug.

check the valves adjustment, and float levels in the carbs, but if those are in spec i would go for a compression test next.