XJ750 won't start :(

Hi guys, I purchased a 1982 XJ750 Seca a few months ago from a PO who had let it sit for just over a year.

I figured it would need some tuning up to get running so I cleaned out the carbs and reinstalled them with the help of an automotively inclined friend of mine.

I recently put the carbs back in but the bike still won't start. It will crank but it won't catch. I'm new to bikes (this being my first one) so I'm not sure what exactly to look for.

Any ideas? What else can I check? Do my carbs need to be synced and if so what's involved?

Thanks!

 

Have you checked your plugs to see if they have spark? Also have you checked to make sure all of the carbs are getting fuel... These are two issues I have run into with my bike.

 

Replace the plugs, as they are cheap and gets that out of the equasion.

The XJs will crank over with a weak battery, quite alot of cranking too! The problem is that there is not enough juice left over to fire the coils.

Make sure the battery is charged (using a low amp trickel charger, a normal car charger can cook a bike battery).

You could carefully jump the bike from a car battery, not with the car running and make sure the ignition of the bike is off when you connect leads. A cars charging system can fry the bikes ignition components. Be very careful not to earth the positive if you do this!

If these don't work we can go from there.

 

I thought that the battery might be low so I'm charging it now. We'll see how that goes. If it's still a no-go, I'll see about replacing the plugs. I should note they were replaced just before the bike was parked by the previous owner, how often should they need to be replaced?

 

I would also check your fuse box for corroded or loose connections I've had two yamaha's were If you held the fuse just right it would start and run, let go of it and it would die. I replaced the fuse box with some water proof spade fuse holders from fleet farm. There are also some places were you can get a new fuse block, search around on this site I know there's plenty in here on the subject.

It might be a place to look, The two bikes I had cranked over fine but wouldn't start, fixed the fuse boxes and they worked great

Well that's my 2 cents anyway

 

Yeah, that would be the next thing to look at. The fuse box will give problems sooner or later. Mine was not giving problems but I replaced it anyway. Then I would go through all the connections and switches on the bike and clean them all. Check for damaged wires too. Even if your bike goes without doing this a bit of preventive maintenance can save a walk home.

 

When I first got my XJ it would not start. Had been sitting for a while. Changed to new plugs and away she went.

Another friend had a CB900F that he did not ride very often, and then he only puttered around (he was scared of it) and was forever having to replace plugs, often he would just clean them. The CB ran fine when I borrowed it a couple of times but I use the throttle.

If you are riding often then the plugs should last a while.

 

Blow some Starting Fluid into the Airbox ... if it pops you got spark.

If it pops ... pull the carbs and clean them.

If it don't ... troubleshoot an Ignition fault.

 

Hi Rick,

Good tip! Would be a good one to include in the FAQ.

Would this work with something like WD40 insted of instantstart?
I ask because many in climates that are not covered in snow several months a year are unlikely to have instant start as part of their normal vehicle kit. Guess it is the either in the instant start that causes the Pop?

 

I think carb cleaner would work better then wd-40

 

Isopropyl Alcohol.
BBQ Starter
Gas
Bacardi 151
Hair spray ... but, its messy

 

Ok so we pulled the plugs (plugs that were in bike were extremely dirty) replaced and tried again, still no catch.

We tried spraying carb cleaner into the air-box while cranking. The bike will catch for a second then die. Sounds to me like it's not getting any gas. We juts cleaned the carb, using Rick's guide. Any ideas on getting the gas to start flowing?

Thanks for all the advice so far!

 

Make sure you have gas coming out of the petcock, They are vacuume operated, Did you try running it on prime, or on. The prime doesn't use the vacuume it just gravity feeds, but when you switch it to on, then it needs the vaccum to pump

If it runns on prime but not on run, I'ld check out your petcock

 

I left it on PRI for 5 mins or so and then cranked it once on PRI to prime the fuel pump. After that I cranked it on ON. Fuel does come out the petcock if the gas line is not connected.

 

Leave it on PRI. If you can start it and run on PRI there is something wrong with the vacume operation of the petcock.
Is there a vacume line attached to the petcock?
There is no fuel pump.

Float levels OK?
Choke working?

 

The UPPER LEVEL feed system needs to be de-clogged!

You need to inspect:

The Fuel Bowls.
The small, "Wells" in the back wall of the Fuel Bowls need to be checked for blockage.
Fill the Float Bowl ... shine a light in well ... if the level of Fuel, in the drilled WELL isn't equal to the level in the Float Bowl ... unclog the Metering Ports at the bottom of the Bowl.

Siphon Tube.
Narrow Brass Tube extending into the Well.
Probe with Cleaning Tool.
Use Tip Cleaner from Welder's Tip Cleaning Tool Set ($3.95 @ Welding Supply or Hdwe Store).
Probe and Clean Brass Siphon Tube extension.
Blow-out with Carb Cleaner.
(Heat Shrink Tubing, Model Race Car Fuel Line or Model Plane Hose will slip over the Brass Tube and allow the Carb Cleaner Red Tube end to line-up and Blow-out the tube with the spray)

When you get the Top-End Fuel Supply all unclogged and flowing good ... you have it ready for fine-tuning!

 

I've found that old guitar string works great for cleaning out small passages and jets, put a small kink in the guitar string and feed it through and work it back and forth while twisting the string in a circle. then shoot carb clean through it and then some compressed air. It's worked great for me. you don't want to get to aggressive with it you want to remove any junk not the surrounding metal.

 

sooooo.... i'm having the same problem this guy was, my 1982 seca 750 had a rusty tank and i mean seriously rusty, got rid of the rust in the tank changed inline fuel filter cleaned carbs, they looked clean but the screens for the float bowl assembly valves were nasty i cleaned the screens sprayed carb cleaner everywhere in the carbs, now i am going to try and re-clean the carbs because the bike just cranks, HOW strong does the battery need to be-- I try starting the bike now while hooked to a car battery (yes the car is off) with the bike battery dead and being hooked to the car, is there enough juice for the coils? the petcock is on prime there is a small inline fuel filter. how do i check the fuel levels in the bowls?

 

1. get your battery load tested at a local auto parts store
2. how did you clean your carbs? (search for "in the church of clean" and "the whole nine yards" for carb cleaning info on here
3. do you have a service manual?

 

Proove your petcock, by sucking on the vacum pipe you will see the fuel running if working OK.