82 xj 750 will not start

the bike spits and sputters but wont run clean the carb 3 times and a rebuild kit still nothing the guy got it from said it run in the fall but would only idle im getting spark please help

 

Unfortunately most of us has found that any statements of mechanical status and running ability by previous owners is bullcrap.

I would first do a compression test on the engine to insure that it is a viable plant.

If that passes, then pull the valve cover and check your valve clearances are in spec, if not, put them in spec.

Cleaning carbs...vague description, If you dipped the entire carbs in carb cleaner for a soak, the throttle shaft seals and fuel rails seals are destroyed, as well as the pilot o-ring and the float valve. It will never start until you do an entire rebuild and church of clean.

Did you wet set the floats?

Did you do a good bench sync?

are the mixture screws turned out 2 1/2 for bottom?

Did you replace the spark plugs?

This is what I had to do to get my bike to run, then came more fine tuning and tweaking.

A shot of starting fluid could help also.

Also, set the choke to full and don't touch the throttle. These bikes just hate when you try to throttle them during a cold start.

Hope this helps

 

+1.

Heed the voice of experience (thanks Bruce, you saved me some typing.)

There is a lot more to carbs than just cleaning them; and your valve clearances need to be in spec to properly adjust them afterward.

Invest in a service manual; you have some work to do.

(Once it's running, we need to discuss the brakes.)

 

so I did the compression test I got 75 100 105 90 not sure what that means hopefully you help me

 

Those numbers are not good. We need a "second opinion."

The first step will be to test again, and be sure you use a DIFFERENT gauge, and have a fully charged battery, all spark plugs out and the throttles held wide open. (And unplug the TCI so it doesn't self-destruct.)

If you get similar results, then do a "wet" test. By that I mean add 1 ~2 TEAspoons of oil to each cylinder, and re-test. See what happens to the numbers.

We'll go from there. The next step will probably be to check the valve clearances; depending on what you find the clues may be there (stuck valves, or...)

But get a new compression test, and a wet one too.

 

I did wet test on it the numbers are 150 185 160 140

 

Urk.

A change like that tends to point to rings/cylinders.

You're going to decide how much money you want to spend. Rebuilding that motor will probably cost more than replacing it.

I'd still run another set of compression tests.

 

I did a wet test again with the throttle wide open I got 160 175 160 150

 

Right. But "wet" numbers significantly higher than "dry" numbers indicate a problem, usually with rings/pistons and or cylinder walls.

Wait a couple of days. In the meantime, check the valve clearances. Test again. Consider doing a "leak down" test.

 

Does this apply also if you dip the whole carb in an Ultrasonic cleaner?

 

If the fluid in the ultrasonic was non caustic to rubber, probably not. How ever, the throttle shaft seals and fuel rail seals are 32 years old if they are original. I didn't do mine on the original cleaning, only to have to go back and do them after 3 months of riding. My suggestion is to do them now and use silicone grease on the reassembly. It isn't a matter of if they leak, just when..

hope this helps

 

I agree with Fritz in that the rings are not seated but all hope is not lost. That engine will run with those numbers. Maybe not well and it would be a bitch to tune but it will run if your carbs are right and the valves are in spec. Pull the valve cover and check the clearances. Pull the carbs and read Len's church of clean write up. Once you have the carbs right it should run. While you are getting acquainted with those carbs, and yes you need a manual, put 1 ounce mix of 50% ATF and diesel fuel in each cylinder and let it sit. When you are ready to try for a start blow the mixture out of the cylinders clear buy motoring the engine with the plugs out and the TCI disconnected. It's going to make a mess so be ready. Also when it dose light off its going to smoke like an old Volvo. It will go away so just be ready. Once you get some heat in it and its best if you can ride it for 50 miles or so, check your numbers again. Bet they come up to spec. If not now you know you need to go into it. Saved a couple of engine tear downs this way. Good luck.

 

Where you at in the northeast? I just went through this whole thing with my 82 xj750. So if you need some help rebuilding the carbs I might be of assistance. But you are more than likely going to have to buy a carb rebuild kit. I recommend Len from xj4ever (banner top of screen). Best 280 I spent on the bike was the deluxe rebuild kit with metal tip needles.

 

Where you at in the northeast? I just went through this whole thing with my 82 xj750. So if you need some help rebuilding the carbs I might be of assistance. But you are more than likely going to have to buy a carb rebuild kit. I recommend Len from xj4ever (banner top of screen). Best 280 I spent on the bike was the deluxe rebuild kit with metal tip needles.

 

Thanks for the response. The liquid used was not caustic to rubber (dish washing liquid). I have planned to replace all the fuel rail seals, but not the shaft seals....but you are right in saying having gone that far, I may as well eliminate anything else rather than wasting time having to remove, dissemble and replace anything a second time around.
Cheers

 

I retested the it today I got 75 -140-135-125 dry

 

Check your valve clearances. If #1 is anything better than dead tight on both intake and exhaust, something is definitely wrong in that pot.

 

what do you mean by better than dead tight?

 

no clearance between cam and shim, basically touching each other so nothing can be fit between two. I am supposing that if there is no clearance, the valve may be open a bit when it should be closed and this would give you low compression numbers in that cylinder.

 

This is a very good definition of "dead tight", lol!