XJ400S Starting issues

[DanR]

Hi,

I was riding the other day and knocked the bike down a gear to get past something and the engine just had no power and then went to a complete stop. It was as if I had ran out of fuel - which I hadn't. Anyway got recovered back home. The bike had been standing for a few years likely with the same fuel in so though it may have been that. I have drained the tank, carbs and stripped the fuel hoses but couldn't find anything that untoward.I have checked the spark plugs and compression all ok. When I put the petcock in purge and open the carbs reservoir outlet no fuel comes out....

My next line of investigation is whether the petcock is supplying fuel as well as the vacuum "fuel pump" after the petcock. Is the best way to do this just take off the fuel hose supplying the engine turn it over and see if fuel comes out the hose?? 

Also there is a solenoid (number 3 in the picture attached) that actuates a hose that goes from the carbs to the engine head on one side what is the solenoid for?

Thanks for your help in advance.

Cheers

Dan 

[slice]

Your fuel tap should have something like "OFF" "RES" "FUEL". The fuel only flows when your on the fuel setting normally BUT if you chose RES then it should piss out regardless, your bike needs a vacuum from the engine to draw fuel from the tank to the carbs, you only use RES if your a tit and forget to fill up (been there done that.!) The pipe from num 3 carb is the Vac pipe, you should have a filter somewhere in the fuel line to, might be under the tank? Something like the pics below.

Of course you might have none of this as your bike is totally different but that's the usual fittings on a lot of bikes. Hope that helps a bit anyway.

Those are just generic pictures yours might be slightly different.

  Fuel tap   And Filter

[jimmy]

If vacuum carbs, it should say On / Res / Prime. It should run freely on Prime ( I assumed that's what you meant when you typed purge, but maybe not)

So answering your question "Is the best way to do this just take off the fuel hose supplying the engine turn it over and see if fuel comes out the hose??" my answer would be Yes, but only after you have confirmed that the petrol is coming through the petrol tap (petcock) and running into the pump

[DanR]

Thanks guys, yes sorry I meant prime - I gave it a go and fuel came out. I am going to strip the carbs and give them a good clean. I have seen two separate posts about xj400's with the same issues and both times it was just dirty carbs. Going to drop the oil, get new filters etc too to see if that helps. 

Thanks again 

[jimmy]

A dirty carb you say?

[DanR]

Hi all,

Thanks for your suggestions. It has taken me some time to get on with the bike but I have done the following:

• Cleaned fuel lines and tested the vacuum fuel pump (took the hose supplying the carbs off and it pumps fuel).
• Stripped and cleaned the carbs
• Dropped the oil and replaced with new inc filter
• Changed the air filter
• Re-assembled
• New fuel

The bike still won't start ! I have checked the sparks - I am no expert but there is a spark on each plug. They all seemed pretty dry as if no fuel was getting into the cylinders. It turns over and splutters now and then as if trying to start but wont.

I don't have a compression meter but tried the old school way to see if there was any compression at all by holding my thumb over the spark plug hole - each one pops my thumb off. 

I am at a total loss. I was hoping that the events which lead up to when the bike stopped working would help. Like I said I gave it some welly and it bogged and came to a stand still as if I had ran out of fuel / fuel starvation. I have tried feeding the carbs direct with fuel from the tank and plugging the vacuum lines which made no difference - read on another post that if this worked it shows that it is a fuel supply issue.

Any suggestions would be greatly appreciated. 

Cheers

Dan 

 

[drewpy]

Have you checked the valve gaps and timing?

no1 piston @ tdc should see both valves closed on #1and trigger on alternator just at the ignition point

 

might also be a weak spark = no spark under compression

[DanR]

Hi drewpy,

Thanks for the quick response. I did check the valve clearances - sorry I missed it off my list, they were all ok. I did not check the timing however..... bugger I'll have to strip it again! By the time I got to checking the clearances in the Haynes manual I'd had enough.... maybes I should revisit it. When I was testing one of the spark plugs for spark the bike did back fire but only once and it didn't happen again - It nearly gave me a heart attack! My friend said that it could be a timing issue.

If the timing is off is it an easy job to rectify? I read that the bike has an auto tensioner - I will have a read over the manual and give it a shot this week sometime. 

Thanks again.

Dan.

[jimmy]

6 minutes ago, drewpy said:

might also be a weak spark = no spark under compression

+1 for that. Have you tried new plugs. Although dry, do the old ones stink of fuel or not. Do you have pics

 

 

[DanR]

Hi Jimmy,

Sorry missed that off my list too! I changed the spark plugs - I am not sure if I still have the old ones but will check, they were pretty black/brown. The new ones are still white and dry even after a full day of fiddling and then trying to get it to start about 30 times at least. It was end of play today when the battery went flat after being charged last night!

Cheers 

Dan

 

The other thing that didn't help is it was a very bright day today so checking the spark was a bit difficult - there was one there but hard to see. Is there any other way of checking if you are getting the right spark than lying the plug on the engine body?

[drewpy]

if they are dry, no fuel, carbs may be sticking shut of full of dried/stale fuel.

 

keep spraying some easy start in the air box and if it sort of starts, its the carbs

[DanR]

Perfect, thanks I will give that a go

Cheers

[jimmy]

22 minutes ago, drewpy said:

keep spraying some easy start in the air box and if it sort of starts, its the carbs

Just reading Drewps post and had a thought. On the carb inlet manifold there should be rubber bungs which are removed to fit vacuum gauges??? If so try removing one of them and spraying the easy start in the cutting out the carb altogether. That would definitely confirm carb issue

Not sure if this can be done, but if so..........

 

Or try this

 

 

[DanR]

Hahaha I could have done with this today - frustration was at an all time high. I'l give it a shot and report back :). 

[DanR]

Hello again :D,

I tried the easy start spray and the bike fired up and kept going. I stopped it and left it about 30 mins and the bike started without any help!

It was idling way too high so I reset / lowered the idling screw and redone the the mixture screws on the carbs back to what it advises in the manual as I had been fiddling yesterday.

The bike idles good now however when I rev it with the throttle it takes a long time to recover to idling speed 5 - 10 seconds or so. I can hear the throttle cam on the carbs resetting and the accelerator isn't sticking! The butterfly valves were also closing fine. What could this be? 

Also when I rev above 3000revs the oil light comes on. I just changed the oil and have checked the level and it seems to be correct. I did use 10W30 which is an option in the manual the other was 20W40 which I could not find in the store I was in. I am in the UK so rarely get nice weather but it is 20degC today.

Thanks again,

Dan

[finnerz89]

Probably an air leak if it's slow to rev down

[drewpy]

or carbs need a clean inside. spray your easy start around the intakes and if the revs rise because it it, there's a leak so you need new intakes.

 

otherwise it might be best to send your carbs away to be thouroughly cleaned inc jets. I've used NRP in manchester as they are close to me.

[DanR]

The plot thickens!!

I have called it a night for now but will give that a go with the spray tomorrow. I think I did a pretty good job on the carbs but perhaps not - just before I put the bike away I noticed the exhaust wasn't very hot. After looking closer cylinders 2 and 4 are not firing - going to look at the carbs and floats tomorrow :S.

Thanks again.

Dan

[DanR]

Hi,

So after a fresh pair of eyes from a mate, a bit of a conflab, new battery and a compression gauge (all ok) we saw that the slide in carb 4 was not oscillating at all! We found I had missed one of the o-rings in the top of the carb (the opposite end of the fuel bowl) luckily I found it in my tool box doh!! 

We also consulted the wiring diagram and found the correct order of the spark plug cables - there are two coils one on the left of the bike and one on the right, you would assume the one on the left fed cylinder 1 & 2 and the one on the right 3 & 4 but no...... left = 1 & 4, right = 2 & 3. I change them over!

The bike starts fine without any splutter, first time and all cylinders are firing - however 1 & 3 exhaust are considerably hotter than 2 & 4 although all are too hot to touch.

Getting somewhere at last!

I am still getting a slow rev down when I rev the engine - I am going to try and reset the fuel / air needle adjuster and check for air leaks in the rubber manifold seals - I hope they are ok as they are pretty expensive for a bit of rubber!

Cheers

Dan

 

[drewpy]

thank feck for that, your driving me nuts with all these Q's