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Discussion Starter #1
First of all, I tried to post this in the technical section, but my limited access only allows me to post here. So here we go. Hopefully someone can help.

A 2002 VT750 ran perfectly for years. Then it sat for 4 to 5 weeks. Now it will start up on full chock, but dies if you try to open the throttle.

4 to 5 weeks is not really enough time for the gas to clog the carburetor jets. But just to cover all bases, a pint of SeaFoam was dumped in the gas tank while the engine was running on full choke. Then it sat for a few days to let the SeaFoam work, but no change.

All signs point to the engine not getting enough gas. But it idles nicely on full choke. As soon as you try to open the throttle, you get a carb fart and the engine dies.

It looks like this beast has a fuel pump on it. Are the fuel pumps prone to failure? If the fuel pump was defective, would it still run on full choke?

Has anyone experienced this problem before?

Any suggestions for troubleshooting? I do not have a repair manual.

Thanks...
 

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Did you check your air intake for leaks? Also make sure your carbs are sitting nice and snug in the boots. Sometimes it's the simplest thing that's causing the issue. I've experienced it.
 

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all of the above could be causing your problem.
pull the fuel line from the pump, place it in a bottle and crank it see if you have flow, if so unscrew the drain on the carb bowls make sure they have fuel in them, use something to under them to catch any fuel that may come out, and be carefull.
if so pull the carbs and clean them real good, all jets and passages.

heres a link for the ACE manual, the other 750's are also listed in the general discussion section on this site.
http://www.hondashadow.net/forum/53-general-discussion/99631-honda-service-manual-ace-750-a.html
 

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More likely the pilot jet (or slow jet as some call them).
I'm with you. Probably clogged idle/pilot/slow jets. That does not mean that there may not be other issues related to gummed up carbs (stuck needles/passages and/or floats), but usually, when you clean up the pilot jets, you clean up the rest of the carbs at the same time. That is where I would start.

If you do not want to remove the carbs, you can always start by removing the pilot jet adjusting screws and squirting some carb cleaner in there (and of course reinstall and adjust to 2 1/2 turns out). That can put some cleaner closer to the gummed up idle/pilot/slow jets. You can also try removing the carb-to-airbox boots to check the functioning of (and partly clean) the vacuum piston diaphragms. Also check the intake boots for tightness while you are working on the carbs. That is about all you can do with the carbs still on. Otherwise, you got to R&R the carbs. Really not very hard. Less than an hour to remove, go through them, and replace.

If you haven't changed your fuel filter in a long while do that too.
 

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More likely the pilot jet (or slow jet as some call them).
Almost guarantee that's it. Based on the sitting and the systems. Just went through it with mine. Get some seafoam or BG 44k and run it through it. The 44k is a little better in my opinion, but its much higher priced. Or just clean the carbs. The pilot jets are small enough to clean with a strand of copper wire.
 

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Discussion Starter #10
Thanks guys!

I will pull the gas line at the fuel pump and check for flow first. If I have a good flow of fuel at that point, I will know the fuel filter and fuel pump are good. No use fixing/changing what is working fine.

After that, I will have to dig into the carbs. I look for the easy stuff first. Much more work getting the carbs off and cleaned. Just hard to believe that sitting 4 or 5 weeks would cause them to get clogged up.

What I am not hearing from the group is any known problems with fuel pumps. I guess that is good, but replacing the fuel pump would be a lot easier than cleaning the carbs.:)
 

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Thanks guys!

I will pull the gas line at the fuel pump and check for flow first. If I have a good flow of fuel at that point, I will know the fuel filter and fuel pump are good. No use fixing/changing what is working fine.

After that, I will have to dig into the carbs. I look for the easy stuff first. Much more work getting the carbs off and cleaned. Just hard to believe that sitting 4 or 5 weeks would cause them to get clogged up.

What I am not hearing from the group is any known problems with fuel pumps. I guess that is good, but replacing the fuel pump would be a lot easier than cleaning the carbs.:)
It runs with the choke on , so you know your atleast getting some fuel to the carbs, FP most likely not the cause, but start there and you can eliminate it from the equation.
 

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Discussion Starter #14
I thought using THAT much seafoam at once was a bad idea?
A long time ago I ran out of gas and all I had in my saddle bag was a can of SeaForm (or some other carb cleaner). So I dumped it in my tank straight and it got me to the next gas station. Bike ran pretty good and did a nice job on the carbs... I think I was riding a Harley at the time. Go figure...
 

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One other item to check is the vacuum port screw on the intake boot (where manometer hooks up to)....is it gone? This will cause HUGE vacuum leak.


I bet a hundred bucks it's the carbs dirty though.....

BTW, use the bowl drain screw to verify gas in carbs...not the fuel pump line. I'm getting out on a limb not knowing the specifics of said bike model, but fuel pump only runs while engine is rotating on most....not just key on, keep that in mind.
 

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Had the same problem when I did the bean box mod. Bike would run at idle on full choke. Then sputter from idle to 1/8 throttle. Then it would run fine from 1/8 on up. My slow jets were completely clogged. I used a strand from some wire to clean it out. I needed to put in a larger slow jet anyways(42) but after that the problem was fixed.

You are not getting enough fuel at idle. See if it still happens after 1/8 throttle when your main jets and fuel needle start to take over.
 

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Discussion Starter #18
Had the same problem when I did the bean box mod. Bike would run at idle on full choke. Then sputter from idle to 1/8 throttle. Then it would run fine from 1/8 on up. My slow jets were completely clogged. I used a strand from some wire to clean it out. I needed to put in a larger slow jet anyways(42) but after that the problem was fixed.

You are not getting enough fuel at idle. See if it still happens after 1/8 throttle when your main jets and fuel needle start to take over.
I am sure I don't need to change any jets... I have not modified anything. It also ran perfectly (just like a Honda) before it started to act up. I might have to clean them but definitively I don't have to change them.

Also, this bike dies when I open the throttle... It does not sputter. It dies...
 

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I think someone has already mentioned the fuel filter..But you could be wasting your time cleaning the carbs if the filter is full of crap..you could just block the carbs again..

John
 

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I think the bike is pissed that you let it sit... buy it some chrome and try again.

Consider pulling the plugs... if the bike is running rich it wont take long for the plugs to foul. If you have been running with choke on for 5 or 10 mins then they should be fouled. I'm with you. Gas shouldnt gunk a carb after 1 or 2 months. I think you have a vaccuum leak.

If you fmessed with your air mixture screw in the past... make sure it didn't pop out... that would cause sudden change.
 
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