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Discussion Starter #1
So, i've got some issues going on regarding most ranges of RPM but also some serious problems mid-range and higher.
Whenever I pull off idle the bike seems to sputter and bog without any real reason. On throttle, it surges, bucks, dies, restarts and wont rev past half throttle or seems like it's only running very limited, and takes me being in 5th gear just to get to 60mph which is insane.

I've completely replaced the fuel lines, fuel filters, cleaned every part of the carb, and checked float levels to make sure they're in spec. The Jets are the same size i've always had and i've done no major modification to the bike at all to justify these issues going on. I did replace the diaphragm slides with (Amazon.com: MTOP RACING Membrane Diaphragm Carburetor Vacuum Piston For Honda VT750C Shadow A.C.E. 1997-2001 VT750CD Deluxe 1998-2003 VT600 VLX400 NV400 Steed VLX600 NV600 Steed VF500F Interceptor VF500C Magna: Automotive) these back in November, but they're still completely in tact, and they worked fine after originally replacing them so I didn't think it was that.

I've been chasing this problem kinda going through the diagnostics for awhile now, compression is fine in both cyls, and I was going to get a leakdown tester to do next but figured i'd ask around here before doing anything as you guys are pretty good at this.
 

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VT 1100c 1994
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Did you check the main jets, pilot jets (blowing or looking through them)? Maybe you have forgotten something when you put everything back together. I made some mistakes when I did the jetting and assumed that, eg., groove nr 5 doesn't work, which was wrong and I did something wrong with the carbs.

The easiest might be to clean the carb again, get new jets (not expensive) put it back together.You can spray break cleaner over the carbs when idling to see if there's a leak. But it sounds like clogged carbs to me.

When did the problems start, and did you do something w. the bike at that time? Does the 750 have a fuelpump and or did you check the pump?
 

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Discussion Starter #3
Did you check the main jets, pilot jets (blowing or looking through them)? Maybe you have forgotten something when you put everything back together. I made some mistakes when I did the jetting and assumed that, eg., groove nr 5 doesn't work, which was wrong and I did something wrong with the carbs.

The easiest might be to clean the carb again, get new jets (not expensive) put it back together.You can spray break cleaner over the carbs when idling to see if there's a leak. But it sounds like clogged carbs to me.

When did the problems start, and did you do something w. the bike at that time? Does the 750 have a fuelpump and or did you check the pump?
I cleaned every nook and cranny possible on it, the pilots are brand new, but the main jets are not. Though I did take my compressor and after completely cleaning it with carb cleaning go through and spray 20PSI Air through every hole possible.

It does have a fuel pump, I was going to check that next but it clicks and runs fuel through it when it seemingly needs too pretty much indicating to me that it working; I can check anyways though.

I don't remember exactly when it started, just that it started within the past 5-6 months.
 

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Not sure on the exact procedure but it comes up often here on how to flow test the fuel pump and bypass the fuel pump relay to eliminate them as your problem.

I'm sure someone with the method will chime in but you can make a jumper wire for the fuel pump relay and test ride the bike to see if it makes a diffrence.
The fuel pump flow test is letting the pump put fuel into a measuring cup.and time it.
Its supposed to put out a certain amount of fuel in a certain amount of time.

Rule those items out and move on if they past the test.
I though my carbs were clean as well,the third time was the charm for me.
Also check the flow of fuel from the petcock valve.Perhaps the in tank filter is clogged not letting the pump get enough fuel but if that was the case the pump would make a louder ticking sound.On that not verify that the tank vent hose is not clogged up with a mud dobber nest.Clogged vent means fuel will not flow through the tank.
 

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New thread just posted with the fuel pump test specs.
28 oz per minute of fuel
 

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Discussion Starter #6
Not sure on the exact procedure but it comes up often here on how to flow test the fuel pump and bypass the fuel pump relay to eliminate them as your problem.

I'm sure someone with the method will chime in but you can make a jumper wire for the fuel pump relay and test ride the bike to see if it makes a diffrence.
The fuel pump flow test is letting the pump put fuel into a measuring cup.and time it.
Its supposed to put out a certain amount of fuel in a certain amount of time.

Rule those items out and move on if they past the test.
I though my carbs were clean as well,the third time was the charm for me.
Also check the flow of fuel from the petcock valve.Perhaps the in tank filter is clogged not letting the pump get enough fuel but if that was the case the pump would make a louder ticking sound.On that not verify that the tank vent hose is not clogged up with a mud dobber nest.Clogged vent means fuel will not flow through the tank.

I'll test it out in a bit, I cleaned all vent holes of any potential issues prior for sure. Petcock is also clear and fuel flows perfectly fine.
I've suspected the pump, but kinda put it off as not possible since the fuel still gets to the carbs and fills the bowls or so I thought
 

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1983 Honda vt750 Shadow
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Did you alter the factory intake?
What color are the spark plugs?
Get up to 3000 RPM and hold it there even if it is in 2nd or 3rd gear and ride a 1/2 mile. Stop and pull a couple of plugs to see what color they are at the problem RPM/speed.
 

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Discussion Starter #10
Did you alter the factory intake?
What color are the spark plugs?
Get up to 3000 RPM and hold it there even if it is in 2nd or 3rd gear and ride a 1/2 mile. Stop and pull a couple of plugs to see what color they are at the problem RPM/speed.
Factory Intake is all stock, and the plugs were white on the electrode, but a glazed brown along the ring outside of the electrode.
I'll check the plugs after a hard hold at 3k RPM, thankfully the road that goes right next to my house is exactly 1/2 a mile :^)
 

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Discussion Starter #11
Okay, sorry about the 5 day delay.
Life took over for a bit lol.

That was the plug right after a straight run, and after taking the carbs apart I notice literally not a damn speck of dirt anywhere, it's basically spotless internally.
Since the removal of the plug, I did reset the timing advance mod I did like a year ago back to as stock as I can get it, and it still runs exactly like before so I know it wasn't that, otherwise I have absolutely 0 idea.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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That must be frustrating as hell, it seems everything is good.
Glad to see you are not just throwing parts at it.
Did you check the carb boots for leaks?
That one often gets missed.
 

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Discussion Starter #13
That must be frustrating as hell, it seems everything is good.
Glad to see you are not just throwing parts at it.
Did you check the carb boots for leaks?
That one often gets missed.
Yea, I sprayed around the boots with some starting fluid and not a lick of intake issues, which isn't surprising cause I replaced the old hard boots a year or so ago with new ones.
Air box is stock with the exception of a Hiflo, but I replaced that 2 whole years ago so it messing up now would be weird, considering it's also pretty damn clean too.
The carbs are sync'd and done so meticulously that it's within 1 notch of each other.
 

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1983 Honda vt750 Shadow
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That plug is too lean.
Are all 4 the same color?
Try turning the mixture screws out to about 3 turns as a trial.
The low speed circuit usually controls only up to about 1/4 throttle but may be a help to see.
The float level can affect mixture if out of specs.

 

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Discussion Starter #16
That plug is too lean.
Are all 4 the same color?
Try turning the mixture screws out to about 3 turns as a trial.
The low speed circuit usually controls only up to about 1/4 throttle but may be a help to see.
The float level can affect mixture if out of specs.

Mixture screws were already pulled to 3.5 which didn't solve anything unfortunately.
And the floats were put to perfect 7mm spec


right, which jet-size is in use? Didn't she used to work (or am I mixing up sth)?
Using DJ Stage 1 Jet kit since I have Vance and Hines pipes; And yes it did work with this exact same jet set.

42 Pilots - 102/106 Mains DJ (R/F)
 

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Discussion Starter #17 (Edited)
Alright, I tested the pump as per how it says in the Manual.
Andafter 5 seconds i almost get 4oz, I multiplied on the minimum which is around 3oz and still got higher than spec pump at 36oz a min. I'm thinking it's probably the fuel relay possibly, i've got a doner relay which is known working and will be putting things back together to test drive after finishing cleaning the carbs again.

Hopefully this clears up the issues.

EDIT: It's off of a Saber 1100 sitting in my car port that I use for parts, idk if this makes a difference but I figured i'd point that out.
 

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Discussion Starter #18
Alright, I tested the pump as per how it says in the Manual.
Andafter 5 seconds i almost get 4oz, I multiplied on the minimum which is around 3oz and still got higher than spec pump at 36oz a min. I'm thinking it's probably the fuel relay possibly, i've got a doner relay which is known working and will be putting things back together to test drive after finishing cleaning the carbs again.

Hopefully this clears up the issues.

EDIT: It's off of a Saber 1100 sitting in my car port that I use for parts, idk if this makes a difference but I figured i'd point that out.

Well, this fixed a FEW issues seemingly; the main ones being the stuttering at low RPM is for sure gone, but i'm still having this mid/high-range problem where it seems to bog down.
And I still can't figure out why. I am considering taking the carbs off of the 1100 to see if I can use the Diaphragms from those on the 750.
 

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1983 Honda vt750 Shadow
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Check your spark plugs for color. White is too lean and black soot is too rich.
 
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