Hard starting

Hello,
I bought a 1983 xj750 maxim in March this year. The bike has 15,000 miles and sat for 10 years before I got it. I rebuilt the carbs, & changed plugs and intake gaskets and air filter, and cleaned the gas tank. The compression was 125 lbs. each cylinder. It ran good for the first 3 months. Now I am having trouble with starting it. It takes 8 to 10 starts, each time running a little longer, until it finally stays running. Once it is warmed up it runs OK. Choke linkage is operating.
Any help greatly appreciated.
Don

 

Got to find out what is causing the problem.

Sounds sorta like fuel starvation, as in a delivery problem, but the mirror of that is an extreme lean condition that persists until warmed up. I can think of reasons for both, I've seen some weird stuff.

When cold and on choke (enrichment), it drinks fuel like crazy. If the fuel supply can't keep up, it will stall periodically. As the motor warms it requires less fuel for a stable idle, so the problem goes away as engine temperature comes up.

It seems to me the problem is in the fuel line, tank, or vacuum petcock circuit if it stalls the whole motor out like it ran dry, as opposed to unusual high on-choke idle speed, which is a good indication of a massive air leak.

Make sure the petcock vac line is not kinked, collapsed or split...maybe put a clear filter in the fuel line so you can actually see if you are losing supply when it dies out, or dealing with a different problem...

Make sure the fuel line isn't kinked or making a bend it can't handle, not split and sucking air, etc.

I don't know if these have a screen on the petcock...I would assume so...check that too.

 

PS you try starting with the petcock set at different positions?

Reserve pulls from a lower intake point, if the problem is in the primary supply, this might show you a difference.

Also the "PRI" position on mine allows fuel flow without engine vacuum...try that too if you have it...if nothing changes doing this stuff, the petcock or tank can probably be ruled out...

 

Did you happen to adjust the valves yet? That mileage is when you'll start having problems if they are untouched.

When you rebuilt the carbs, what method of synchronization adjustment did you use afterward?

IN ORDER:
-check/adjust valves.
-carbs cleaned, pass the "clunk" test.
-float levels checked and adjusted using the "clear tube method" and fuel; dry setting is only a starting point.
-bench sync.
-running vacuum sync. (YICS blocked.)
-ColorTune or alternate method for fine-tuning mixtures.
-re-check vac sync.

If you skipped any steps or took any shortcuts, then you know what you need to do.

 

Thanks to all who replied re: hard starting. I'll try your suggestions.
Don

 

Hello all,
After trying things the members suggested, It appears I was using too much choke & causing a flooding condition. Now I start the bike and gradually increase choke as needed. Two or three starts now & I'm up & running. Thanks to all who responded.
Don

 

You never answered re: valve adjustment.

 

I haven't checked valve adjustment as of yet. I need to read up on the procedure for doing that.
After o/haul of carbs, I made no synchro adjustments at all other than idle adjustment. Many of these things I am still learning about.
Thanks, Don

 

maybe dumb question... but which valves are you speaking of and where are they? and how do you adjust them?

 

The intake and exhaust valves; they live in the cylinder head under the valve cover; and the checking and adjustment procedure is explained in detail here: http://xjbikes.com/Forums/viewtopic/t=14827.html

With some additional info here: http://xjbikes.com/Forums/viewtopic/t=29209.html

They need to be checked every 5000 miles on an aircooled XJ.

 

thanks so much for the speedy reply fitz, can you explain some symptoms of the valves needed to be adjusted?

 

Hard starting, long warmup, been more than 5000 miles since it was done.

If you don't have hard factual evidence of a valve adjustment within less than 5000 miles of where you are now, CHECK THEM.

Neglected, a tight valve will become a burnt valve.

 

sounds like a plan, thanks for the awesome write up. I will get on that this weekend.