More 1980 Spitfire problems... Bogging, won't run when hot

[jdcanada]

Here is the background:

1980 Spitfire with Kawi motor - butterfly carb.

Starts great, runs extremely well (was told had motor recently resealed)
Once hot, it bogs and dies. will restart when it cools down, back to same type of operation.


Here is what I have done... started cheap, then started spending money.

Plugs - tried various heat ranges
Cleaned and inspected spark plug caps
Cleaned card very well checking all operation
Made sure tank was venting properly
Replaced fuel pump gaskets - pumps fuel fine
Checked muffler to make sure it wasn`t plugged
Swapped to a Mikuni round slide (I had sitting around) - ran same (great when cold - bogs and dies once hot)
Bought complete coil / CDI with wires (used) - no change
Bought another complete coil / CDI system (in the chance that the replacement used coil was defective as well) - no change
Replaced rectifier

All of the above had zero resolution on the problem. As a backyard mechanic kinda guy, I know may ignition issues appear as carb (fuel) problems thus the reason I was looking at both areas.

I am now thinking it must be the stator. Am I looking for input as to if this is the next logical step?

Please help! Spring is getting closer and my son has yet to have the fun in the snow I promised him three months ago.

Any assistance is appreciated.

Thanks in advance

[ljm]

I would be suspicious that the stator is the issue

[75522]

Have you checked the fuel tank? There is a hose inside the tank that rots out over time. If gone, will idle ok, then starve for fuel as you give it throttle. Also, I would check your crank seals... I have a 79 Spitfire that had the same issues... Tried all the same things you did, and had to replace seals. The PTO side was leaking just enough, that at higher RPM, it would bog and die. Once the seals were replaced it runs like a top!

You can check under the PTO side shaft for oil, debris, etc. If present, then you need new seal...

[smitfire]

Stator?

[JDT]

Free Air engines don't like warm temps.

The colder it is the better they run.

Also slow speed driving limits air flow across the heads to cool the engine only furthering the problem.

I wouldn't even start it up if it was above 20 deg F if it was mine.

[That Girl Racing]

Normally a bog after it warms up is either a crank seal or coil. You changed the coil. Spray some ether behind the clutch and around the case halves and intake areas.

[jdcanada]

I suspected the crank seals but confirmed again from the gentleman I bought it from that he just did them to prep it for sale. A while back I did the either spray around many engine areas by the clutch side as well as intake boot (in the case of a leak could not detect by eye). All okay... did not escalate rpm. maybe I didn't get close enough with the either spray?? Do I try that again? I thought a leaking crank seal would have it run horrible all the time (or not at all). When it runs it does not "lean out" like what I would suspect a leaking seal would do.

To further explain the problem: It starts fine cold, runs fantastic for the first two or three minutes... no issues whatsoever. Then it bogs, then it will eventually die. Wait a bit, it will start up easy enough. Its like its running out of gas but the fuel is in the line and pumping great. Even when it dies, I try to quickly rip out a plug and test for spark. It does spark, maybe not as nice as it should, but that is difficult to truly determine.

I can only think that at this point after everything I have checked, it must be the stator. Correct me if I'm wrong but a bad stator would have the spark break down once hot and or under load... no? This is why i am leading to this conclusion.

So today, I fabricated a flywheel puller and removed the flywheel. The stator "looks nice" if that means anything (its not dirty, with corrosion or obvious signs of a visible fault - but I guess that means nothing). I can go to a local guy and get the stator rewound and sealed... not cheap, but at this point, it really doesn't matter. It has become personal... this thing won't beat me!

Does going to get the stator rewound sound like a wise next step? Am I missing something obvious... or not obvious?

The light at the end of the tunnel is that when it runs when it first starts up, it is a great sled. Its exactly what I need; small, light, quick, simple.

Thanks again to all for any assistance and opinions.

[Steven Rempel]

A few questions and thoughts (not sure I will be of any help or value)

After engine starts and then runs for a few min, can you keep it running by spraying fuel (ie like pumping a primer, I have a old oil can that I fill with mixed gas and it has a pump to spray a bit of fuel in to carb) I sometimes I try this to confirm a lack of fuel or too much fuel and confirmed a bad carb. But I mostly deal with walbro carb. I used this method last week which help identify a weak fuel pump.

After it dies and you pull the plugs are they , wet ,dry, black,brown or white?

what is the engine compression? are they two far apart, I dont know the spec but some engine must be within 10 psi from one cylinder to the next and over a set number, not sure what your engine is speced for.

if you leave it outside till stone cold, will it run longer before dieing?

If you had the flywheel out giving you good access to see the seal, Have you tried a leak down test, and confirmed with soap and water, or maybe there is a crack or something isn't sealing? I have had a engine with new seal from the PO but he damaged the lower crankcase and air was getting in casing a poor fuel air mixture. I only found this well under a 6psi positive air test and lost of bubbles.?


Again not sure if these thing will help but these are the questions I would get answers to before spending and money into a engine I did not rebuild my self. Just my thoughts.

[That Girl Racing]

Squirt some gas in the carb when it bogs. That will tell the tale. The reason they will run until they warm up with a bad seal is...... the cold seal kind of holds it shape. Once it heats up and becomes pliable it does not.

[smitfire]

I got used stators. Will be cheaper than rewinding I'm sure.

[sledhead16]

I'm always very suspicious of previous owners claims unless it's someone I know and trust. So it doesn't start hard like a lot of pulls? Crankseals will usually cause hard starting

[75522]

I would agree with Sledhead16... I got my Spitfire from a guy who is the lead mechanic at a local Yamaha Powersports dealer. Swore it was in great shape, rebuilt carb, etc...

Carb was crap (missing o-rings, dirty, etc) and oil seals were toast.

After a new carb and replacing oil seals, it runs like a champ!

I learned the hard way, replace the oil seals no matter what...