Old bike won't start when hot.

[Anonymous]

I purchased my first bike about a month ago... a '79 GS425E w/ 18k miles. Previous owner had the bike for only a year, so I don't have much history. The bike appears to have been well cared for, and the previous owner is an enthusiast so it seemed like a good investment.

My only complaint is that the bike is difficult to start once the engine has warmed up to operating temperature. It cranks fine, sometimes sounds like it 'wants' to fire. After sitting for 5 minutes or more, it will start. Idle adjustment may need set higher too, because it wants to stall shortly after being parked. This hard starting / stalling when warm is a problem at stop signs / lights if I'm not careful about keeping the rpm's up. I'm not too interested in holding up traffic for 5 minutes while I wait for the bike to cool down!

I should mention that the bike fires right up when cold & choked.

I've read other advice on the web... everything from plugs to valves to coils to points needing set or replaced. I can't spend a ton of $$ on repairing the bike, so I want to be smart about fixing what's broken... not necessarily replacing parts until I find something that's broken.

If anyone's got any ideas, I'd love to hear 'em!

BTW, what can I expect to pay for a tune-up on a bike like this. Are valve train checks & setup part of a typical tune-up?

Thanks...

[Anonymous]

Hard starting problem

Bentjeep,the first thing i would try is if you get a circumstance when it will not start when it is hot.....get the bike to a place where you can pull one of the plugs out....stick the plug back into the spark plug wire boot and ground it against the engine while you turn the bike over with the starter motor.Watch the end of the plug and see if you get a nice fat spark?If you have no spark ,sounds like you have a coil going bad.Once you check the enjine to see if the ignition system is working properly you can find the culprit through a process of elimination.....check coil first,pickup coil or points and ignition amplifier if its electronic ignition...also make sure all electrical connectors are clean and tight...good Luck!....Larry

[KEITH KRAUSE]

I always advise checking the electrical connections first too, because it's easy and should be done periodically. Check the connections at the coils/leads/plug caps for corrosion and make sure they're tight. Clean and re-gap the plugs if they are in good condition. Replace them if the center electrode is rounded/worn or the ground electrode is wearing short. Check/clean the battery connections and fill the battery with distilled water if it's low. These are quick and easy things to do.
You may be having fuel starvation or a fuel flow problem too. Here's some more quick and easy things that should be done and don't cost much or anything. Clean or replace the air filter. Clean the vent in the gas tank cap. Replace the petcock vacuum line if the hose is getting hard or even has small cracks. Make sure the fuel line is not kinked. If you have an in line fuel filter, I recommend removing it and running just a straight fuel line. If the tank is rusty inside, the tank should be repaired. If you put the petcock lever to "prime" and this fixes your problem, then you have a failing petcock diaphragm and the petcock will need to be rebuilt or replaced. Remember to turn the lever from prime when the bike is not running. The carbs side air screws may be set wrong. They should be set to achieve the highest rpm and then re-set the idle to 1,100 rpm with the idle screwknob. Put the bike on it's centerstand and warm it up first. Turn the screws equally in 1/4 to 1/2 turn increments and listen for the rpm's to max' and then re-set the idle as I said. Use a marker to mark where your screws are if you need to put them back. They are generally 1 1/2 to 2 turns out. They may be stuck, so use a good fitting tool.
If you still have a problem, the carbs need checking. Beginning with the float needle valves/seats.
But as stated earlier, check the electrical first and make sure the sparking is good.

[SqDancerLynn1]

Carry an extra spark plug Just plug it in when the problem happens
Other wise follow Keith's advise

[Planecrazy]

Some good advice was given on a somewhat similar problem with my '80 GS550 and you might want to try it first. On my bike, after it runs for an extended period at highway speed (higher RPM's) the bike starts to bog down and eventually dies. After five to fifteen minutes it starts right up and runs somewhat normally if I keep the speed down (lower RPM's). It was suggested to me that the fuel cap vent might be clogged, and as the engine runs a vacuum is created in the tank that starves the engine of fuel.

Next time you warm up the bike and it starts to become tempermental, try opening the fuel cap and see if you hear a "whoosh." If you do, try starting the bike right afterward, and if it starts right up you've found your problem ... clogged fuel vent in the cap.

Hope it's that simple! Haven't had good enough weather to check mine yet, but I already replaced all the ignition components so I know it's not electrical on my bike.

Good Luck!

Steve 8)

[rosco15]

I've been doing a bunch of jetting changes on my bike lately. I noticed when a had a large pilot jet in the bike that it started great when cold, but when it was hot it didn't want to start. I had to crack the throttle a bit to get it to fire. I wonder if your getting too much gas from your mixture screw setting. my .02 cents

[KEITH KRAUSE]

I've been doing a bunch of jetting changes on my bike lately. I noticed when a had a large pilot jet in the bike that it started great when cold, but when it was hot it didn't want to start. I had to crack the throttle a bit to get it to fire. I wonder if your getting too much gas from your mixture screw setting. my .02 cents

Yep, it could be that too. You never know what a used bike has had done to it.

[Motorcyclemodeller]

If your bike is actually stalling when it is hot...........it is too hot. When the motor does not want to stay running at idle, the motor is way to hot. Everthing has expanded too much and tolerances are decreased, when you try to start it everything is so tight it can not move quick enough to start.

Anyway there is an easy fix............your plugs are to hot!

Either the wrong plugs are in the bike or you need to go to colder plugs. Go one plug colder and this should eliviate your problems.

Hope this helps!

Dr. Dre

[RacingJake]

Does your bike have points? Check your timing

If it does install new points and condeners. sometimes the dwell can be off and the engine will start fine when cold but once hot the timing may be to far advanced. Condenser's can act up too (short out) when they get hot.

[jimcor]

Old biker won't start when hot...??????

Needs Viagra!!!



Now how's that for an 800th post?!

[RacingJake]

Now how's that for an 800th!

Well I'd need Viagra too if I did it 800 times.

[jimcor]

Nice edit job Racin'Jake!!

[Anonymous]

Well seems to have been the points. I checked the plugs for spark when hot, spark plug gap, & gas tank vent. All seemed OK, so I started on the points. The gap was a little narrow, according to the spec.s, so I adjusted & cleaned 'em. Static timed it, and now it starts right up when engine's at running temp. Thanks for the advice!...