Topic: 1988 Yamaha FZ750 UPDATE: CDI QUESTION

[hoodellyhoo]

Anybody know anything about these bikes? Trouble spots? Helpful hints?

A roomate of mine (who is less mechanically inclined than me) just bought one for cheap. It has deffinitely been trashed like so many older sport bikes, but is a solid project.

The issue right now is that it won't start. My roomate rode the bike to our house (20 or so miles) and then parked it outside. Last week it rained and now the bike won't start at all. No huffs or puffs, nothing. Once in a great while it will pop out the muffler. He said it was a hard starter, but it would always start eventually.

We pulled the plugs and they were wet with fuel. We tested for spark and had decent spark. We pulled the gas tank and airbox and sprayed starter fluid down the carbs...got nothing. It just doesn't make any sense to me. We have spark, we're getting gas, it ran two weeks ago. I would think we'd at least be getting something in the way of combustion.

One of the problems is that my roomate has essentially no budget so buying anything for this bike is hard for him to do. I found a downloadable owner's manual on fz750.com, but we don't have a shop manual. He did buy new spark plugs and a fuel filter today so we wil try that on wednesday. If that doesn't help, then I'm running out of ideas.

Anyone have some wisdom to share?

[ColinMc]

Well i have 3 of them in parts...lol. Great bikes, nothing was unplugged? One of the CDI plugs can be easily plugged into the wrong thing and then it'll never start. Another place to check on those bikes is the starter solenoid, they tend to go bad...does it turn over no problem?

Oh and btw, the valve adjustment on those is a royal PITA! 5 valves per cilinder is NOT fun lol. But slap some pod filters on, a stage 3 jet kit, a kerker white tip exhaust and you have a killer running bike. I LOVE those bikes.

If you are sure you are getting fuel, it must be spark...is the cutoff switch working properly? Try toggling it back and forth a few times, sometimes they gum up. It COULD be a compression issue, but if he rode it somewhere right before it happened then it rained it's probably just crud got in somewhere...better yet how old is the gas? Did water get in the gas tank? Is the fuel pump pumping ok? It'll make an clicking when it's pumping. It should click the second you turn the key on it the cut off switch is in the run position and continue clicking when you are trying to start it.

[hoodellyhoo]

Nothing was unplugged on the bike. When we put the plugs against the block we got spark. We took the #4 spark plug and tested it in all four wires and got spark. The bike turns over no problem (except after we drained the battery, so we jumped it to my 350f).
I tried toggling the kill switch a few times thinking it was dirty, but that didn't help.

 The gas is probably only three weeks old at the most, he ran a tank or two through it before he rode it down here. I doubt any water got into the gas, seems like everything was water tight. Is there a way I could know for sure?

Judging by what you said about the fuel pump, it should be okay. My roomate asked me about a clicking noise he would here when he turned the key on. He said sometimes it lasted longer than others. In all of our fooling around it would only click once or twice. Even if it is not working properly, I would guess that it should still fun for a few seconds on the starter fluid.

I really hope this isn't a compression issue, it's be such a big bummer for my roomate because he's so strapped for cash. Unfortunately it seems like a possibility because he said it was always a bit of a hard starter. But if that was the case, I don't see why having it sit out in the rain would magically make it not start at all.

BTW, I downloaded a service manual for it, but it's in german .

I am trying to find any info I can on FZ750.com, but their forums are more combersome to use and there's very little activity there.

[ColinMc]

Does the choke work ok? That cable can bind up sometimes...it's a tough starting bike when it's cold. You might need some throttle too to get it going...unless you flooded it which is also a possiblity lol. Do the slides move ok?

[ColinMc]

Is the fuel tank vent tube kinked somewhere? I forgot about that one...The fuel pump doesn't always click the same amount. As long as it does click you are in good shape. Can you see fuel in the inline fuel filter? Mine is always about halfway full. I have a sneaking suspision the carbs got gummed up or the choke is messed up though...Probably from him riding it and crud from the tank, even though its relatively fresh gas the crud in the bottom of the tank probably got sloshed around and got in the mix.

WAIT! how much gas is in the tank? Try switching the reserve switch to the reserve position, or put more gas in, those switches go bad sometimes...

[hoodellyhoo]

I don't believe the vet tube was kinked anywhere, I did check to see that it was open at the end.

There was fuel in the fuel filter, along with a fair amount of crud. I wouldn't be surprised if the carbs are crapped up a little, but I would still think we'd be able to get some kind of combustion from the starter fluid. The slides move nice and free but who knows about the internal passages.

There was plenty of gas in the tank before we took it off. We also tried switching between on and reserve.

If there's one thing that I've learned, it's that I will be forever grateful for my bike. Everything is (comparatively) easily adjustable and fixable. Everything is easy to access. Man, and I though changing spark plugs was hard on my 350f...

[ColinMc]

Lol, yeah i usually take the radiator and tank off the FZ to get easier access....but man is it a pain.

So I guess the only thing left is the choke not working right...or a float stuck in one of the carbs. I'm surprised though because i've had ones that ran like crap on carbs that were junk...but it still ran.

Can you smell gas if you take a whiff of the exhaust pipe after trying to start it for a while. Or better yet, when you changed the plugs or checked them, did you hook the wires back up correctly? The wires are a weak point too, where the boot connects to the wires.

[hoodellyhoo]

I'm pretty sure we were smelling gas out the muffler when we were trying to start it.

The wires were on correctly when we tried starting.

I don't know if it makes a difference, but when we first pulled the boots there was rain water down by the plugs. We left the boots off for a night to let it dry out but that still didn't help anything. We still had spark with the plug against the block, but maybe the water down in the plug holes was shorting something?!?

[bryanj]

Its worth fitting a new set of plugs as although they may spark outside they can fail under compression

[ColinMc]

Good call, make sure you get ALL the moisture out of those boots and out of the spark plug wells too.

[hoodellyhoo]

We might be working on it again today. I would think everything has had enough time to dry out, but I will make sure all is well before we start putting it back together.

BTW, thank you guys for helping. It is much appreciated.

[ColinMc]

Check on the condition of the boots/wires too...like i said before they tend to come apart.

[hoodellyhoo]

Alright, we just got done working on it for a bit (ran out of daylight).

before we put the new plugs in we made sure everything was dry (boots, plug holes, etc). We made sure that the wires were securely in the plug caps. We also made sure and gaped the plugs correctly.

This netted nothing from the bike. We tried starter fluid and got nothing again.

We pulled the #1 plug and I wouldn't say it was wet or smelly, but that could have been because we didn't crank it all that much. Not sure how wet it should be after a given amount of cranking.

As long as the plug was out, we cranked it to check for spark. Spark seems good to me. It's certainly blue. Either way, while we were cranking it sputtered a bit and kinda ran for a second or two.

We put the plug back in and tried various things while cranking it. We again got another brief moment of "running" but mostly nothing.

We know that the fuel pump is working because we could see the fuel go down in the funnel we had hooked up.

So I'm kinda stumped again. We're going to pull the carbs tomorrow and see what's going on in there. Is there a way to check that everything in ignition land is working properly? IE, should I have a big fat blue spark? Is there a way I can check the coils or CDI box with a multimeter to make sure they are in prime condition?

Aside from fiddling with the carbs I'm not sure what else we can do. I just can't get over the fact that it won't fire more with the starting fluid.

[hoodellyhoo]

We finally had a chance to look at the bike again today. We took the carbs off to clean and just for kicks tried starting the bike with starter fluid and no carbs. We got absolutely nothing, which again makes me think this is an issue with spark.

Based soely on what I have read in this forum, I gather that motorcycles from this era had something called a CDI module which did something with spark. Unfortunately these units seem to fail and are expensive to replace.

My question: is there a way for me to test the cdi module or to rule it out as a problem?
Is there anything else I can test as far as ignition problems?

We took one of the carb bowls off and everything looks very clean, making me think they didn't cause any of the starting problems. We're still going to clean them, but I doubt they are the root issue.

[DME]

The best way to diagnose a faulty CDI-box is to try another one that you know is working. Is there anyone in your neighbourhood that is running the same bike? Borrow his. Would definately be worth a try!

You say it´s always been a hard starter:
A problem with Yamaha´s 5-valve engines (FZ 750 and FZR 1000) is that the intake valve seat tend to wear excessively.
That causes the valve to sink deeper and the valve clearence to decrease. When it gets smaller the bike gets harder and harder to start cold.
When it gets to zero you´ll start burning your valves.
Easiest way to check it is to lift your valve cover and check intake valve clearences.
If the wear is too far gone, just adjusting the valves will only fix the problem temporarily. Unfortunately the only cure is to replace all intake valve seats and intake valves..... and there´s 10 of them....

Cheers
Dan