Serviced carbs ran for a bit now won’t start.

Hi everyone. I’m working on a 1985 maxim 700. It had been sitting for a few years so I took the carbs off and cleaned them. I also cleaned the gas tank completely and of course put in fresh supreme fuel. I took it for a ride. It worked excellent but I knew that it needed a throttle cable. I finally got the throttle cable and installed it. I tried to start it and now it won’t start. It cranks excellently, it has spark, the fuel is making it to all of the float bowls but not making it to the cylinders. The spark plugs are staying dry. What could be affecting all 4 carburetors?? Any ideas? Thank you for reading my long winded post.

 

I don't know that bike but any chance you swapped the throttle and choke cables? Have seen that multiple times over the years on here.

 

Which version of the 1985 XJ700 Maxim?
1) XJ700N, "Maxim", air cooled, Hitachi carbs
2) XJ700XN, "Maxim X", water cooled, Mikuni carbs

 

try a shot of starter fluid into the air filter see if it starts.

check in the area where you did the work.
so we can assume the fuel line is connected did the vacuum line slip off the petcock or manifold nipple?
throttle cable not to tight?

are you using the choke?
if no fuel is flowing to carbs with enrichment circuit it could be clogged so could the pilot jets

 

Did you get the right cable? Xj4ever Carrie's the correct cable ..

 

Thanks for the reply but the cables aren’t switchable.

 

Air cooled. Hitachi

 

Yes it’s the right cable I was able to find OEM cable and I compared them just for fun.

 

Have you got an auxillary tank you would use to supply fuel to the carburettors when balancing carburettors. If so try connecting that to see if engine starts.

 

Are your right handlebar switch screws tight. Handlebar switch grounds to the bar l believe on your bike. Should be fine as you have a spark.

 

I will try starter fluid.

The vacuum ports are plugged. But can you tell me why you asked? You might be on to something. Will a vacuum leak prevent fuel from being introduced into all 4 cylinders?
It’s been a bit ago that I repaired the carbs so I can’t remember the ports exactly

Throttle cable is just right.

I am using the choke/enrichment valves. I see what you’re saying but how could all of the carbs have exactly the same problem. Keep in mind that it did run perfectly after the carbs were serviced.

 

Yes I did try that. While engaging the starter the fuel level wouldn’t go down but if I drained the bowls, individually, the fuel did go down so the floats, needles and seats are good.

 

That’s a good point. Yes I do have spark but it is sort of faint in my opinion but a spark is a spark right???

 

Spark looks weaker on an TCI ignition system so it might be fine. I mentioned the right hand switch body grounding to the handlebar because you fitted a new throttle cable and the bike was running beforehand.

It's the dry plugs l keep thinking about. Have you tried the starter fluid mentioned above yet just to see if the engine fires. I know your bike was running well before and these cannot go out suddenly but have you checked the valve clearances?

You can also connect a car battery (with car engine not running) and try cranking the engine. But if the fuel is not getting to the cylinders that won't help.

 

How many plugs did you have out when testing for a spark? Counting from the gear lever side of the bike when plug from cylinder one is out four must be in the cylinder head to ground that coil. Same with plugs two and three. One coil operates cylinders one and four the other coil two and three. You can have a spark when the plug is out because there is less compression so the starter is drawing less current, but the spark ceases when all the plugs are in because the starter needs more power to work against the engines compression. If you have a voltmeter set it to 20V DC and put the clips on the battery terminals with the battery fully charged. Then press the starter button the voltage under load should not drop below 10.8 Volts. You need that to make the transistors work in the TCI unit to produce a spark at the plugs.

 

I meant to say all plugs cannot be out at the same time or the TCI won't be grounded.

 

How clean was the fuel source? No rust of little parts floating in your gas tank? If it was running and then started to act funny and then die, I am leaning to carbs got full of stuff. Might want to drain one of the float bowls with a light color rag under it. That way when the gas comes out you will be able to see if there is any junk in the bowl. Good luck.

 

I’m going to check that voltage. But the plugs are dry. Doesn’t that mean that it’s not getting fuel?

 

I haven’t tried the starter fluid yet. It’s a new battery and I keep it on charge.

 

Yes l think that is a possibility. As fuel is getting to the carburettors it should be getting drawn into the engine especially as your bike was running beforehand.

 

The tank was super clean, The gas is fresh supreme gas, the petcock was cleaning and new diaphragm and o rings put in. New external filter too.
I drained each float bowl to make sure gas was travelling to the bowls and the floats were working properly.

 

Filter that can cause problems. What type is it? Did you fit it before the throttle cable? Is there an arrow on the fuel filter for direction of flow?

 

I even put gas down the fuel line via a little funnel so that bypasses the filter.

 

Can you put the kill switch in the off position. Then crank the engine with the throttle open. The vacuum should draw fuel into the cylinders and make the plugs wet. If this happens l think your float bowl jets could be blocked. The brass coloured tube goes into the float bowl body. At the bottom of each carburettor is a tiny jet that allows fuel to travel up the brass tube into the intake to richen the mixture for cold starting. If you are correctly cranking the engine on a closed throttle and these jets are blocked the plugs could be dry.

 

It won’t crank with the kill switch off. I found that unusual. But it will crank over as if there was a kill switch on.
I still find it so strange that all 4 carbs are acting exactly the same. It makes me think that it can’t be an internal carb problem. But anything is possible.

 

Yes you are right, even if it were an internal carb problem it would not affect them all simultaneously. It is strange how you are getting no fuel to any of the cylinders.

 

open vac line or port would make a lean situation fuel would burn but not explode to start bike plugs would be dry.

if vac line fell off port or petcock no fuel would flow.

if butterflies were open due to tight throttle cable the suction/vacuum created from motor would be lessened due to larger orifice with butterflies open and draw less fuel possibly no fuel through pilot jet or enrichment circuit
also the wider the butterflies are open more air leaner mixture,
throttle grip should have a few mm play before the cable lifts the throttle shaft.

you bike was running you changed the cable bike not running.

i went through this with someone recently no fuel flow past carbs his throttle cable was very tight that when it did start it redlined. losened cable to point of stall adjusted idle knob to proper idle readjusted throttle cable fired up.
this may or may not be the problem but it is the work you did last

 

Jeez, really, read that again over...

 

Sorry, a bit harsh there from me. The last bit - cable too tight might be valid, except that was addressed further up^...

 

OH MY GOODNESS. I FEEL STUPID. ‍♀️ I actually have the tank off so I was feeding it fuel through a tiny funnel so that I could see if the fuel was being taken down. I didn’t put much importance on the petcock vacuum line. I plugged it with my thumb a few times to try it but this time I pinched it off with vice grips and it started with a little spray into the air box

THANK YOU ALL

 

a golf tee or 2 is a good plug keep some your tool box

 

Don't feel stupid. We've all done stupid things.

 

I don’t know if I’m doing this right but I hope that the previous readers read this again.

I thought that I found the problem because the one vacuum line was not plugged. When I plugged it it started right up and took fuel from the carbs. But it only did that once. Now it’s back to not taking fuel again. The vacuum is sealed off at each carb. I have a question about that. If the vacuum is sealed at 3 carbs and open at 1, wouldn’t the 3 cylinders suck in the fuel anyway. The big mystery, to me, is that all 4 carbs are acting the exact same way. What do they all have in common that is causing them to not fuel the cylinders?
Recap. -carbs were removed, cleaned,
reinstalled, synchronized
-ran great until I installed new
throttle cable
-all carbs have fuel in bowls.
-all cylinders have spark
-throttle cable is correct
-can’t find vacuum leak ( but
wouldn’t that be an
individual carb problem?)
-using fresh premium fuel
-fuel system totally clean

any advice please

 

Had a similar problem with an xj550 bad fuse holder was preventing proper voltage to ignition box and was not starting. Even though I did get a spark at the plug there was no spark when under cylinder pressure. Also check voltage at battery when cranking. Less than 10-10.5 volts box won’t fire coils.

 

To clear up the mystery, the vacuum line to petcock only allows fuel to flow out of the tank , via the petcock, to the carbs. All four carbs get the fuel from the one fuel line, none from the vacuum line.

 

What height did you set your floats at?

 

Does the switch unit that the throttle cable is fitted to have a proper earth onto the handlebar? Oops looking back at the thread I have asked you that already .

 

This is an interesting question. I eyed them up and they were all exactly the same height. So I left them alone. What are you thinking?

 

This could be the problem, I bench set mine to 17.5mm , float needles tips can dry out and get a groove on them this can effect float height as well not much but still there . If the float height is low you may not get enough fuel on float bowl. What you could do put a container under the float bowl drain screw collect pour it into a measuring cup see if all are the same. To wet set you need some clear hose on the drain nipple , open drain screw hold hose up to the top of carb float bowl should be within 3mm , there are some threads on doing this , Hogfiddles can help you with it .

 

I’m thinking “ if the plugs are dry, there’s no fuel getting to them. There’s only one way for it to get there.... through the fuel valve. If the floats are closing too soon, fuel won’t get through. It explains a startup, because you will have fuel get through initially While the floats are down, but then after the bowls fill up more they close and the level isn’t getting low enough for them to open again.”

 

check the wet set then adjust as needed

Setting the fuel levels

 

What do you mean by fuse holder

 

I’m still a bit stumped as I’m reading through. Am I reading that all 4 vacuum ports are capped? If so, your petcock has no vacuum to operate it. Without a vacuum line, you need either to set your petcock to PRI, or get an “on-off” style petcock.

also, check to make sure your tank cap vent isn’t plugged.