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Discussion Starter #21
I always check for boot leaks with spray carb cleaner, it might be worth a check after it has warmed up for those 10 minutes to eliminate that.
A mechanic I learned a lot of stuff from used to use a acetylene torch.

If that check doesn't show anything unusual I'd up size the pilots to 38's and reduce the main jet on the rear cylinder by one step and see what happens.
You have boot burner or backdraft pipes on that don't you?
Yep. No leaking. I’ll install the 38 pilots. Then do the rear one size down - 140 to 138 keihin.

you are correct about the backdraft
289192
 

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Discussion Starter #22
@CSRoad

went out with your prescribed jetting. It was slow to pick up speed until 1/4 throttle but exactly at 1/2 throttle in all gears it would sputter and have no power all the way up to Wot still no power.
I will say it did now have the water drop / glug noise at idle which was a nice treat.

here is the front plug after the 15 min ride:
289195
289196

When I pulled the plugs and put them back in to get home that front exhaust did kick out one black cloud of smoke quickly
 

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1999 Shadow 750 ACE VT750CD3 Modified
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It doesn't seem to be making the progress I was hoping other than it is getting to WOT


Those plugs don't look too bad, could be richer for power.
How about the rears that were black?

Make sure your idle is up in the 1000 rpm range using the cable stop screw, you need it that high to maintain oil circulation.
A burbling from the exhaust is cool, a slow chugging idle is the way to murder an engine.

This is all going to be a bunch of trial and error there is no definitive answer, the different exhaust pipe lengths will have an effect on main jet selection, the shorter rear is a reverse of the stock exhaust situation. IIRC the stock VT600 uses a smaller diameter primary pipe on the rear exhaust port to balance things out.

Try going up one more pilot size, raising the slide needles a notch too, no need to cut the top off the needle if it is too tight for the plastic retainer just snip the pin shorter on the plastic retainer, making sure you leave enough to retain the spring. Make sure you have a washer on top of the needle e-clip so that it doesn't grab the spring.

BTW have you checked your float heights? Should be 7.0mm as a starting point.
 

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Discussion Starter #24
It doesn't seem to be making the progress I was hoping other than it is getting to WOT


Those plugs don't look too bad, could be richer for power.
How about the rears that were black?

Make sure your idle is up in the 1000 rpm range using the cable stop screw, you need it that high to maintain oil circulation.
A burbling from the exhaust is cool, a slow chugging idle is the way to murder an engine.

This is all going to be a bunch of trial and error there is no definitive answer, the different exhaust pipe lengths will have an effect on main jet selection, the shorter rear is a reverse of the stock exhaust situation. IIRC the stock VT600 uses a smaller diameter primary pipe on the rear exhaust port to balance things out.

Try going up one more pilot size, raising the slide needles a notch too, no need to cut the top off the needle if it is too tight for the plastic retainer just snip the pin shorter on the plastic retainer, making sure you leave enough to retain the spring. Make sure you have a washer on top of the needle e-clip so that it doesn't grab the spring.

BTW have you checked your float heights? Should be 7.0mm as a starting point.
It’s been raining for the past few days so I couldn’t get out.

here is the back plug from the other day:
289260


I just went on the highway for 3 minutes and it spudders hard and absolutely no power after half way pull.

I pulled the plugs this is back plugson highway for 3 minutes:
289261


Here below the first pic is front plugs from the other day and the second pic is the same plug after 3 minutes on the highway:
289262
289263


I didn’t change anything but the idle rpm to a bit higher. Just thought I could try and get a quick coffee at backroad motors. Now my bike won’t go faster than 5kmh after the highway and lots of popping on acceleration
 

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1999 Shadow 750 ACE VT750CD3 Modified
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That front plug looks way too lean after the highway run.
Something strange is going on here and I'm completely missing it.
Is your fuel pump working and delivering enough volume, there is a test in the Service Manual.
WHat is the largest main jet pair you have?
 

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Discussion Starter #26
That front plug looks way too lean after the highway run.
Something strange is going on here and I'm completely missing it.
Is your fuel pump working and delivering enough volume, there is a test in the Service Manual.
WHat is the largest main jet pair you have?
I did pull the seat a while ago and had it running to listen to the fuel pump to see if it hissing (I read that the hissing is one sign of failing) but never pulled the line to see how much gas was spitting. I think I’ll do that.

also while I was broken down on the side of the road. Since the front plugs looked super lean again I just switched them out for a new pair and it would sputter still anything over 5kmh. Then I changed the back plugs too and it runs fine (I’m keeping it under half throttle to get myself home).

So the back may be an issue?
 

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Discussion Starter #27
That front plug looks way too lean after the highway run.
Something strange is going on here and I'm completely missing it.
Is your fuel pump working and delivering enough volume, there is a test in the Service Manual.
WHat is the largest main jet pair you have?
Largest main jet pair I have is 145s

after putting the newplugs in and riding home (under half throttle and no gunning it for 15 minutes) this is what the new plugs are saying:

front plugs:
289265


back plugs:
289266
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Check that fuel pump output as shown in the manual with the relay shorted out.
If its good then put a 145 in the front and back let's see what happens this time.
I was discussing the situation with a fellow enthusiast and he said it may have to keep going even higher on the main jets until it behaves at full throttle.
 

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Are you 10000% sure the vacuum slide diaphragms have no tears or pinholes in them? Check them super closely and pull at the area around the slide where the rubber attaches to see if there are any separations or cracking, I ask because I see you mentioned replacing the lower boots that mount the carbs but I see no indication the diaphragms have been checked or replaced.
 
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Are we even sure the front is running at all? When testing my bike, my father was revving it and saying how good it sounded. That’s when I covered the front intake with my hand and it roared to life. He was convinced both cylinders were firing, When it had only been the rear firing. It can be a little hard to tell...
 

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Discussion Starter #31
@CSRoad I'm going in on Wednesday to the DIY moto garage up the street (Moto Revere) and will check the fuel pump and hopefully it works and ill throw in the 145s, would you suggest keeping the pilots at 38 still? my next biggest pilot is 42 then 45.

@Froth You could be onto something. When this all started its when I put in the dynojet needles... I was extremely careful BUT I never closely inspected the diaphragm. Is there a trick to check for tears/holes? Or just have to look closely. Side note: I did order new carb slide assembly when I read that a couple of days ago - as this bike is old and I'm slowly replacing everything. Still interested in knowing if there is a trick to check because that shipment will be here in a couple of weeks most likely.

@Troy Jollimore I assume its running since the most recent pic above is 15 minutes of light riding under 1/2 throttle. While the pics before that it was a mix of rich and lean. Plus lots of air being pushed out the exhaust... I would think its running if I'm feeling air, no?

So here is my next step - I go in Wednesday to the DIY shop and will be running through this list of things... Please let me know if there is anything I am missing or should try too.

1. Check fuel pump, put new fuel filter in
2. Switch again to new boots (this time OEM) and check leaks with carb cleaner
3. Take out carb, pull it all apart and do another ultrasonic clean
4. Inspect diaphragm
5. Change jets if fuel pump works
6. fit some foam filters for the velocity stack (looking where to get that, if you have any suggestions)
7. Sync carbs again
8. Compression test again

Anything else you can think of would be greatly appreciated while I have all the tools with me at that time.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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I usually manage to burn a finger on the heat shield and mess up the chrome on the pipe.
"Yep it's running now!"
 

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Discussion Starter #35
@CSRoad real time updates hear - fuel pump is pushing 1.64 us qt ... manual wants .76 us qt. I’m assuming this is a minimum and 1.64 is good. I did it three times all with the same reading.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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@CSRoad real time updates hear - fuel pump is pushing 1.64 us qt ... manual wants .76 us qt. I’m assuming this is a minimum and 1.64 is good. I did it three times all with the same reading.
Tthanks for the update plenty of volume and consistent, that possibility is eliminated. (y)
 

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Discussion Starter #37
Tthanks for the update plenty of volume and consistent, that possibility is eliminated. (y)
So today went decent. Minus the small fire getting half way to the garage... rectifier wires touched the battery 😐.

fuel pump is good, fuel filter is changed. I ultra sonic cleaned the carbs again putting them in for 15 mins then blowing compressed air doing this 4 times.

note that just before getting to the garage it started bogging on me and could only go 5kmh again.

after the carb clean I put it back together but used the same size jets as my time was up and I wanted to at least get home. It started just fine, good idle, revved easily in neutral. Then when I rode away. It wasn’t bogging and only in between 1/8-1/4 it would skip/jerk and I’d hear my carb make a pop sound on the left side every so often. But when I was at 1/2 and just above the bike could hall ass again...

Is this a lean pilot symptom? The carb pop.

also for anyone who has more information... I’m now slightly confused on measuring float height. The service manual is garbage. It doesn’t say how to place the carb to measure really.
 

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Discussion Starter #38
Are you 10000% sure the vacuum slide diaphragms have no tears or pinholes in them? Check them super closely and pull at the area around the slide where the rubber attaches to see if there are any separations or cracking, I ask because I see you mentioned replacing the lower boots that mount the carbs but I see no indication the diaphragms have been checked or replaced.
Checked the diaphragms and they look perfect to me. I still have the slides and diaphragm coming to be sure.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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This kind of drags on but he ends up working on the same type of carb and there is some good direction for the measurement proceedure and what to avoid.
It is maybe easier to follow than the service manual as that is really written for mechanics and sometimes assumes a lot.

I measure my float heights using the tail on a digital caliper on both sides of the float, but a float gauge is the correct tool for the job.
 

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Discussion Starter #40
This kind of drags on but he ends up working on the same type of carb and there is some good direction for the measurement proceedure and what to avoid.
It is maybe easier to follow than the service manual as that is really written for mechanics and sometimes assumes a lot.

I measure my float heights using the tail on a digital caliper on both sides of the float, but a float gauge is the correct tool for the job.
Okay I did use a float gauge and it’s at the proper height. Good video too!

I put in 42 pilots and 45 mains. Still the same issue. I’m noticing all the sputtering with no acceleration, it’s all around 1/4 throttle this happens right now.

289377

maybe I’ll set the needle to be richer by one?
 
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