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Discussion Starter #1
Hello all! I have taken the time to research threads, and have tried to determine exactly why I am having some power issues with my 750 Spirit. None of the threads seem to match the problems I'm having, and I would like to list some specifics with my problem. So, in despiration mode I have created this thread it hopes of some feedback. Hopefully I can keep it short and to the point and not confuse anyone. Here are the details:

Model: 2002 Honda Shadow Spirit 750
Problem: No power/ Sluggish Performance after half throttle

When I purchased this bike, the only modifications (that I knew of) was the after market Cobra Exhaust. As soon as I purchased the bike I tore it all apart and bobbed it out. I sent the fenders, covers and tank to paint and got to work on chopping the body and customizing what I could. With that said, I did the following when re-assembling: Added after market air-intake and removed the baffles from the exhaust.

Problems: After I got the bike put back together I went on a 200 mile ride with my buddy. At lower speeds, and in low RPMs, the bike did fine. However, once I hammered down and tried to accelerate it ran like poop. It was sluggish, acted like it was missing, etc.

Original Diagnosis: After a lot of research on this site (and boy was I thankful for all of the useful information I ran across) I narrowed it down to the carburator wasn't getting enough fuel, given the new intake and removal of baffles.

Plan of action: I decided I would order a re-jet kit and change out the jets and needle. So I tore into the carb and discovered that the bike had already been rejetted. The jets were pretty dirty so I soaked them in carb cleaner. I was hoping this was possibly the problem. They were running a 100 and 102 main jet in the carb. I put the carb back together (with a big smile on my face) and just knew I had solved the problem!

Results: Not a lick of improvement. So my buddy and I decided to tweak the bike. I had read that the adjustment screws on the carb should NOT be out more than 4 turns, regardless of any variables. I checked and the left side carb was at 6 and the right side was at 3. I changed them to the 3 turns and the bike would barely run. So I put them both at 6 turns and put a thin t-shirt over the air-intake (in hopes of limiting the air flow). The bike runs great now all the way up to about 7/8 of the throttle then it is sluggish again.

Now I need everyone's input: I have the new dynojet kit coming in Tuesday. It has main jets that go up to 106 and states that I should use the 104 and 106 for the mods I've implemented. Does it sound like the carb still isn't getting enough fuel compared to the amount of air it's getting? Should I put in the max size jets and then turn the adjustment screws back to three turns each? And what is the issue with more than three turns on the adjustment screws? Again, I couldn't get the bike to run unless the screws were back to the 6 turns. Also, I didn't mess with the floats in the carb, nor did I move the adjustment clip/shims on the needle. It was in the 3rd slot, as recommended by the rejet kit I purchased. Should I have moved the shim down to allow more fuel?

I would LOVE to get some feedback....anything at this point! It's riding season and I want to be on the road racking up some miles! Right now that's only possible when I have a thin shirt taped around my intake! :)
 

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check your fuel filter, pinched fuel lines, flow from your fuel pump, and float settings in your carb. if restricting air flow makes it run better your not getting enough fuel. Also since your jets were dirty I reccomend a full carb cleaning if the jets are filthy there is a good chance one or more of the innards of the carb are gunked up too. IMO a full cleaning of the carberator wont hurt and will eliminate that as a possibility. Also reset your carb AF screws to factory settings. and go from there nothing good will come from having the AF scews out 6 turns. if you solve the problem with it so far out of whack you may not have cured the whole p[roblem only gotten it closer.
 

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Discussion Starter #3
Thanks for the quick feedback! Do you think I should go ahead and increase the main jet size to the 106/104 jet and do a full cleaning? This was my first time in a carb....so anything past removing the jets and cleaning just the jets, I left alone. I'm not going to lie...it was a little scary with so many small parts for me to mess up :)

I do have a friend that has volunteered his time, and use to have a bike shop. I just wished that Honda made the carb easier to work on and remove. Man was it a booger to get that thing out!
 

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Thanks for the quick feedback! Do you think I should go ahead and increase the main jet size to the 106/104 jet and do a full cleaning? This was my first time in a carb....so anything past removing the jets and cleaning just the jets, I left alone. I'm not going to lie...it was a little scary with so many small parts for me to mess up :)

I do have a friend that has volunteered his time, and use to have a bike shop. I just wished that Honda made the carb easier to work on and remove. Man was it a booger to get that thing out!
I wouldnt increase jet size until I confirmed that as the problem because you may not actually help the problem at all if its just something plugged up in the carb or a weak fuel pump.
 

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Discussion Starter #5
Sorry for all of the questions here (because my knowledge is limited), but aside from removing the bowls and jets like I did, what else would I clean on the carb? Should I take it to the local Honda shop and have it completely submerged and shaken to ensure everything is completely out? Then throw on a new fuel pump? Or, should I trouble shoot one at a time so that I can narrow down the problem? IE: Completely clean the carb and put the bike together for a run. If that doesn't help move on to the fuel pump and rerun?
 

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You do realize that tossing out jet numbers is near meaningless unless you also state the MFG for each jet. Each MFG of jets uses different numering system for jets and even when jets are the same diameter they may have a different internal taper and flow rates. DJ recomendations are usually pretty close. I might start there and adjust from there. Pull carbs get a big bowl or a bucket and soak the overnight in 50/50 solution of pinesol, or stronger. then blow them out with air. adjust and instal as per the manual. When you get it running warm it up and do a high speed run. Get it up to the trouble area run there for about 1 mile and hit the kit switch, and stop, pull the plugs and look to see if they show signs of lean or rich condition. you need to diagnose the problem BEFORE you start throughing new parts at it. Heck it could be as simple as stuck choke, or being out of sinc.

Are you sure the issue is NOT ignition system related, weak or cracked coils, fouled plugs, plug wires. or even the charging system, weak batter or connections.
 

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could be that air filter on the bike too, I've herd of a few stories of those types of filters being almost unable to be tuned correctly through 100% of the rpm and gear range just because at higher speeds you get a much greater "ram- air" effect at higher speeds than low.
 

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Discussion Starter #8
I'll pulled the plugs and had a friend read them. He said they looked pretty normal and had a tint of white which means the bike could be running a little lean. I replaced the plugs just in case they were an issue and gapped per the manual.

When I put the carb all back together I did notice that the choke does not want to pull out...regardless of the force you put on it.

Is there any way to check the fuel pump to ensure it's operating correctly? The Honda shop is wanting $142 for the pump....:sad:
 

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Discussion Starter #9
Wanted to put this thread back on top and see if anyone can tell me how to check the fuel filter/fuel pump on this bike.

Also, after talking with the dynojet engineering group, they told me that I definitely needed a stage 3 rejet kit (with no baffles and after-market intake) with main jets at 134/138. Right now I'm running 98/100 main jet. Surely I'll see some improvement, but wanted to check the fuel pump and filter just so I'm covering all variables.

Thanks in advance!


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After reading all of this I think you're on the right path with the jets. Before I jetted mine I had a miss in 5th around 80-85. Rejetted and cleaned carbs and adjusted a/f screws and she runs like a top.


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In all this trouble shooting, did you take a looky see at the diaphrams in the top of them carbs???
(Just another possibility that describes the problem/cure for my issue...)
Good Luck
D
 

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Discussion Starter #14
Captain,

Yes. I completely took the carb apart expecting to find stock jets, needles etc. but actually found a stage 1 jet kit. I did look at the rubber diaphragms. However, being relatively new to the carb world, what do I need to look for? I was going to take the carb to the local shop and have them clean and inspect it, but they wanted $155 to put it in a dip tank and change out the o-rings. The carb itself is pretty clean and I sprayed quite a bit of cleaner it it. The bike hasn't been sitting so I passed.

So, what should I look for with the diaphragms? Tears? Holes?


Thanks!


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Sounds like a combo of new airbox/ slightly dirty carbs / unrestricted exhaust woes to me

Here is a link to a jet cross reference chart (as stated earlier, numbers are meaningless unless you know the brand of jet--measure holes with some tiny drill bits to find out what you have before changing)

Keihin, Dynojet, Mikuni Jet Size Cross Reference Tech - The Jockey Journal Board


Here is a very good carb cleaning guide from a forum for old suzukis (but the basics are the same) dont be afraid to tear the carb down just go slow and dont force anything or get in a hurry ----this is a large pdf file

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf


i have heard many stories of mod-ed airbox's and pod air filters causing lots of trouble with fuel air ratios

Clean carbs completely so you know what you are starting with

when i put a cobra exhaust and rejetted my bike the mixture screws seem happy at about 4 turns out---6 turns out is too far, they might fall out (there was still some small popping and spitting on deceleration but when i did the 4 degree timing advance mod, that cleared up greatly)

the majority of your problem is probably that airbox---can you put the old airbox and filter back on and see what it does just for a quick troubleshoot?
 

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Discussion Starter #17
Sounds like a combo of new airbox/ slightly dirty carbs / unrestricted exhaust woes to me

Here is a link to a jet cross reference chart (as stated earlier, numbers are meaningless unless you know the brand of jet--measure holes with some tiny drill bits to find out what you have before changing)

Keihin, Dynojet, Mikuni Jet Size Cross Reference Tech - The Jockey Journal Board


Here is a very good carb cleaning guide from a forum for old suzukis (but the basics are the same) dont be afraid to tear the carb down just go slow and dont force anything or get in a hurry ----this is a large pdf file

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf


i have heard many stories of mod-ed airbox's and pod air filters causing lots of trouble with fuel air ratios

Clean carbs completely so you know what you are starting with

when i put a cobra exhaust and rejetted my bike the mixture screws seem happy at about 4 turns out---6 turns out is too far, they might fall out (there was still some small popping and spitting on deceleration but when i did the 4 degree timing advance mod, that cleared up greatly)

the majority of your problem is probably that airbox---can you put the old airbox and filter back on and see what it does just for a quick troubleshoot?
Thanks for the links! I actually already had the cross-reference chart. When I pulled the carb, the first time, I found that it had a stage 1 kit with DynoJet 100/102 main jets. So I'm going from a .039/.040 to .056/.058 with the stage 3 upgrade. I hope this solves a majority of my problems.

I agree that the majority of my problem is the airbox. I actually thought about putting the old one back on to determine if that was the problem. However, the way the new one interfaces, you have to utilize part of the older intake (the rubber piece that interfaces with the main air box) and it would require cutting out the silicon gasket, re-doing the gasket and waiting 48 hours. So...that might be the next thing I attack after the rejet.

Again, I really appreciate all of the feedback! I'm anxiously awaiting the dynojet stage 3 kit. They only allow one vendor to sell it: Thunder Manufacturing. I wonder why that is....
 

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I know you seem to be going in a direction that's irrelevant, but I really think you need to follow what Captain D said and check the diaphragms and needles. Particularly the diaphragms, make sure you are seating them properly. You have to hold them up in the halfway position while you are starting to reseat them.

If you haven't picked it up yet, you need a Honda Manual, it will give you all the procedures you need to follow with high specificity.

Damian
 

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Discussion Starter #20
Damian, I'll definitely check the diaphragms again. When I did the initial tear down, they seem to be fine, but I didn't give them a thorough look-over. I didn't think to, because before I put on the after-market air intake and pulled the baffles, the bike ran great. I have a Clymer's manual that does an excellent job walking you through the disassembly/reassembly process so I feel comfortable doing that. I have the carb sitting on my work bench waiting on the Stage 3 Dynojet kit to arrive. I'll tear it down tomorrow and do a thorough inspection!

Again, thanks for the help! The knowledge you guys take for granted never crosses my mind!


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