[David C.]

I bought this bike back in Feb. of this year. It had a bad rod knock, so we tore it down and replaced the crankshaft, push rods, and push rod bearings. It is running fine. I can start it, drive it wherever I want to go, but if it's hot, it does not want to re-start. After a bunch of reading here, I decided that the fuel system might be creating a vacuum, so I started poking around. I noticed that the fuel shutoff valve has this vacuum line;



The new fuel shutoff valves do not have the vacuum line;

Honda Shadow Aero Sabre Spirit 1100 Ace Tourer Gas Fuel Tank Petcock Valve | eBay

Does anyone have experience with this problem, or should I be checking another part of the fuel system?

 

[twerth]

The vacuum line on your existing petcock opens the valve automatically when the engine is running and closes it when the engine shuts off. This will keep the carbs from filling your crankcase with gas if a float valve doesn't seal.

The petcocks you're looking at on Ebay are not for your bike. They're for bikes with fuel pumps (as opposed to gravity feed like your bike). The pump won't allow fuel to continually drain if a float valve goes bad, so the vacuum operation isn't necessary.

 

[David C.]

The vacuum line on your existing petcock opens the valve automatically when the engine is running and closes it when the engine shuts off. This will keep the carbs from filling your crankcase with gas if a float valve doesn't seal.

The petcocks you're looking at on Ebay are not for your bike. They're for bikes with fuel pumps (as opposed to gravity feed like your bike). The pump won't allow fuel to continually drain if a float valve goes bad, so the vacuum operation isn't necessary.

So the vacuum hose acts like a fuel pump, creating suction to draw the fuel into the carb?
Do you think that this might have something to do with the bike not starting when hot?

 

[7xclm]

When you start the engine the hose is connected to a port that has vacuum it then moves a diaphragm in side the valve opening the valve. Conversely when you shut off the engine it looses vacuum and closes.

It has nothing to do with the engine not starting when it is hot.

Now when you say the engine will not start when it is hot. Does the starter engage the engine and it turns over or does it do nothing.

How long do you have to wait until the engine cools off enough to start.

 

[David C.]

Now when you say the engine will not start when it is hot. Does the starter engage the engine and it turns over or does it do nothing.

How long do you have to wait until the engine cools off enough to start.

It will turn over, and it has spark but no gas when hot. I have to wait at least 15 minutes before it will start again. This is a problem that I really need to resolve, and I'm not sure where to start looking. (I knew that I should have rebuilt the carb when I had the engine out. That is probably the problem, sticky float?)

 

[swifty2014]

I don't think a float will stick when hot and not at other temps. But that petcock may have a problem and the diaphragm swells and shuts off fuel,-just as guess.
Can you check how much fuel is flowing out of the petcock by putting a vac hose on it, and sucking a vacuum, with a hose to a container, and seeing fuel flow cold, then warm? If it flows well an any time you probably have an electrical issue.
Another fast way to confirm a lack of fuel is take off the air filter and when it won't start, spray some carb. cleaner in the intake and it will run for a short while, if everything else is good.

 

[chuck12563]

No start when hot is also a symptom of failing coils, a common problem on 80's shadows.
Check them for cracks and Ohm them out per specs.

 

[Geaux Ride]

+1 bad or cracked coils

 

[David C.]

+1 bad or cracked coils

I can't see any visible cracks, I just rode it, it will not start. Both cylinders are getting a spark.

 

[smilie]

Open your fuel cap and try it again. Might not be a hot issue at all, but a plugged vent.

 

[7xclm]

This goes against popular thought, but I would replace all 4 plugs first. If it still does not start I would remove the carbs and rebuild them completely. Replace everything except the floats, paying close attention to the A/F screws.

 

[balloonot]

Ok. Admittedly I have never heard of this kind of issue resulting from what you did. I rebuilt my p/c. With that said, You should reinstall the correct p/c. They make rebuild kits for them. So square that issue away first. If it still does the same thing then you have coil issues. I sus[ect that the p/c flaaper valve is not opening. Only problem is it makes no sense to me that it only does it when the bike is hot. So that brings me too COILS..lol

INSPECT THE THICKNESS OF THE SPARK.

Do not mistake a weak spark, for good spark. These 1st gens are very dependent on a FAT spark. Remove the coils from the bike entirely and check for cracks and ohm the primary and secondary sides out as was suggested by Chuck. Check the manual for the specs. I forget off the top of my head.

Next advise is very important too. Disassemble the plug wires.
Clip about 1/4" from the plug and coil side of the spark plug wires to get to new conductors. Use dielectric grease on the plug and coil side to ensure a good electrical saturation is running through the ignition system. While your there regap the plugs too.

 

[Geaux Ride]

Well, I'll tell you about my hot start problems I had awhile back. It would start cold no problem run good; you would stop for say gas and then go to start it back up and nothing, would not start; wait 10 mins or so and it would fire up and run fine. it was driving me crazy, I checked all the same stuff, plugged vent, vacuum lock, spark plugs, bad battery, etc. I searched on here and found someone said the coils. I had look at the spark when hot and it seemed ok, maybe more orange then blue but I didn't think that much about it until i inspected the coils and saw some cracks and then I metered them and they were off in the secondary if i remember correctly. I bought new coils (which are pricey unfortunately) and problem solved.
I'd check the cheap and easy stuff, but if nothing helps go for new coils IMO

 

[Eagle7840]

I bought this bike back in Feb. of this year. It had a bad rod knock, so we tore it down and replaced the crankshaft, push rods, and push rod bearings. It is running fine. I can start it, drive it wherever I want to go, but if it's hot, it does not want to re-start. After a bunch of reading here, I decided that the fuel system might be creating a vacuum, so I started poking around. I noticed that the fuel shutoff valve has this vacuum line;



The new fuel shutoff valves do not have the vacuum line;

Honda Shadow Aero Sabre Spirit 1100 Ace Tourer Gas Fuel Tank Petcock Valve | eBay

Does anyone have experience with this problem, or should I be checking another part of the fuel system?

Bad ignition coil(s). You can verify by checking for spark at the plugs when hot. Oops, looks like you checked that, but sure sounds suspicious.

 

[swifty2014]

Does it sound like it cranks a bit slower when hot? Like the starter is getting tired and drawing more current hot and then the whole system suffers from too much voltage drop? Maybe jump it with a strong battery to eliminate that.

 

[David C.]

Does it sound like it cranks a bit slower when hot? Like the starter is getting tired and drawing more current hot and then the whole system suffers from too much voltage drop? Maybe jump it with a strong battery to eliminate that.

Yes, it does. Almost like riding it is drawing the battery down. I just put a new Yuasa battery in it thinking that might be the problem, but it didn't help.
Must be the coils. I already ordered 4 new plugs since that was the cheapest thing to do, they will be here soon.

 

[swifty2014]

Before you put too much money out on parts, get a meter on the battery to check what the condition of the charge system is in. If you charge your battery at home, and it runs good for a while then things change, it just may not be charging fully.
If the 3 phases of the stator are not all working you may have some charge but not what is needed to run and charge the battery also. Test while running cold to hot,, see what the R/R is doing. A new battery will suffer also the same as an older one, without a good charge rate.

 

[balloonot]

Does it sound like it cranks a bit slower when hot? Like the starter is getting tired and drawing more current hot and then the whole system suffers from too much voltage drop? Maybe jump it with a strong battery to eliminate that.

Yes, it does. Almost like riding it is drawing the battery down. I just put a new Yuasa battery in it thinking that might be the problem, but it didn't help.
Must be the coils. I already ordered 4 new plugs since that was the cheapest thing to do, they will be here soon.

This is very telling. If it sounds like the starter is dragging every time its hot, then I agree with Swifty. You need to rule out the charging system. Heres a couple videos on how to check the stator and R/R.

https://www.youtube.com/watch?v=kDx3zgOLShY

https://www.youtube.com/watch?v=5v2LtHlvcqI

If they check out then go to the coils as said before. Let us know what you find out.

 

[David C.]

This goes against popular thought, but I would replace all 4 plugs first. If it still does not start I would remove the carbs and rebuild them completely. Replace everything except the floats, paying close attention to the A/F screws.

I had my doubts, but I thought lets go with the least expensive possible solution first, and work from there. 4 new plugs later, it starts when hot.
Thanks to everyone for the help!

 

[swifty2014]

Glad it was an easy fix!
Spark plugs are the first thing that starts the combustion process.
You wouldn't think that just a gap between two pieces of metal that look OK would cause headaches.