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Discussion Starter · #1 ·
Took my bike out for some further distances yesterday and got up to about 45 on some bits. The guy I bought my Shadow from told me it had a hesitation issue in higher gears when going up hills. It's not extreme, but the bike seems to just lose it's umph on steep hills when I really roll on the throttle. The engine doesn't have a problem going into high revs in neutral and I don't notice any hesitation in 1st/2nd gear.

List of things the seller did before he sold me the bike:
Cleaned the gas tank, fuel pump and filter. Rebuilt the carb and put in new jets and tuned it back in.

He mentioned that it likely needed new throttle boots and that if that wasn't the issue it may be the diaphragms, but hadn't gotten to those steps yet while the bike was listed for sale. After I got back yesterday I sprayed some brake cleaner on one of the throttle boots and didn't notice any difference in engine sound, but I figure maybe there isn't enough vacuum to notice any potential hairline cracks that could open up under a heavier vacuum.

Question is are there any smoking gun or easy things to check off the list to solve the hesitation when I need a lot of power? Figure I could start checking the plugs or for any vacuum leaks?
 

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What Bike???
Don`t be afraid to "wind her up"...
It`s gotta Rev Limiter which will NOT allow you to over rev your motor...
What you describe relates to Too Slow in Too High of Gear...
MAYBE???

Welcome @MillennialManual
 

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Discussion Starter · #3 ·
What Bike???
Don`t be afraid to "wind her up"...
It`s gotta Rev Limiter which will NOT allow you to over rev your motor...
What you describe relates to Too Slow in Too High of Gear...
MAYBE???

Welcome @MillennialManual
Wow I'm an idiot. It's a 99 Shadow 750 ACE. Has 15k on the odometer and is a stock bike with some highway bars I put on 2 days ago. Also forgot to mention the original owner had changed the oil in there too.

I was wondering in the back of my head if it was just in too high of gear. I think I was in 3rd going maybe 35mph up a somewhat steep hill (I'm in the mountains in SW Virginia). The sensation the bike was giving me still didn't feel right though, but I'm also not used to power curves on bikes. I had an 88 Toyota pickup in highschool that was very underpowered and wouldn't give me the same stuttering feeling if I went up a hill like that in a higher gear, it would just totally bog down and I'd downshift.
 

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Wow I'm an idiot. It's a 99 Shadow 750 ACE. Has 15k on the odometer and is a stock bike with some highway bars I put on 2 days ago. Also forgot to mention the original owner had changed the oil in there too.

I was wondering in the back of my head if it was just in too high of gear. I think I was in 3rd going maybe 35mph up a somewhat steep hill (I'm in the mountains in SW Virginia). The sensation the bike was giving me still didn't feel right though, but I'm also not used to power curves on bikes. I had an 88 Toyota pickup in high school that was very underpowered and wouldn't give me the same stuttering feeling if I went up a hill like that in a higher gear, it would just totally bog down, and I'd downshift.
So, if the bike is stock, why did the PO install new jets, did you ask him?
Where those jets oem replacements or something else (other brand/ebay Chinese rebuild kit).?
I'd look into that (oem jets) as those other jets could cause the conditions you are experiencing.
jmo,
Edit: the front and rear main jets are different sizes, and reversing them during the "rebuild" could lead to problems too.
 

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Discussion Starter · #5 ·
So, if the bike is stock, why did the PO install new jets, did you ask him?
Where those jets oem replacements or something else (other brand/ebay Chinese rebuild kit).?
I'd look into that (oem jets) as those other jets could cause the conditions you are experiencing.
jmo,
.
He didn't give a reason for new jets. I assume they were gummed up pretty bad and the guy that fixed it works at a motorcycle shop so it may have been easier to replace than to clean them. The bike was originally his Uncle's who quit riding so the bike sat in a garage for almost 10 years and had a gummed up tank and fuel lines. Bike has about 150 miles on it since that work was done so I'm wondering if there was any residual gunk that hasn't come out of the system yet.

Aside from that, the bike starts with no choke when it's in the low 70s outside. I know sometimes that can indicate that the jetting is too rich, but the bike has pretty smooth power delivery at low and mid range and no issues when there aren't hills.
 

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I do not hafta use "Choke" above 40 degrees temperature on my Baby...
Stock, Bone Stock motor, with 175,000 miles on her...

Lets RIDE,
Dennis
 

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He didn't give a reason for new jets. I assume they were gummed up pretty bad and the guy that fixed it works at a motorcycle shop so it may have been easier to replace than to clean them. The bike was originally his Uncle's who quit riding so the bike sat in a garage for almost 10 years and had a gummed up tank and fuel lines. Bike has about 150 miles on it since that work was done so I'm wondering if there was any residual gunk that hasn't come out of the system yet.

Aside from that, the bike starts with no choke when it's in the low 70s outside. I know sometimes that can indicate that the jetting is too rich, but the bike has pretty smooth power delivery at low and mid range and no issues when there aren't hills.
If it feels like a miss and not bogging down, I'd change the plugs if they were not changed recently.
Get Iridium NGK plugs, there's 4 of them, pricey but worth it.
Check the plug wires for corrosion at the plug boot end (they screw on).
You can snip off the wire (1/4") to expose new wire.
jmo,
.
 

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Discussion Starter · #8 ·
If it feels like a miss and not bogging down, I'd change the plugs if they were not changed recently.
Get Iridium NGK plugs, there's 4 of them, pricey but worth it.
Check the plug wires for corrosion at the plug boot end (they screw on).
You can snip off the wire (1/4") to expose new wire.
jmo,
.
Sounds like a pretty simple area to check. One of the more likely things in my mind.

Unrelated, I had a tune up on my old 2000 Sierra like 10 years ago and the shop put Iridium plugs in and my truck threw random misfire codes at me constantly. Come to find out GM Vortec engines hate Iridium plugs, but a lot of people swear by them on other vehicles. Are they a big difference from getting OEM Honda plugs?
 

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Sounds like a pretty simple area to check. One of the more likely things in my mind.

Unrelated, I had a tune up on my old 2000 Sierra like 10 years ago and the shop put Iridium plugs in and my truck threw random misfire codes at me constantly. Come to find out GM Vortec engines hate Iridium plugs, but a lot of people swear by them on other vehicles. Are they a big difference from getting OEM Honda plugs?
Honda OEM plugs ARE NGK, iridium plugs would be the same NGK number as OEM.
1999 Honda VT750CD2 A CYLINDER HEAD (RR.) | Ron Ayers
#36 spark plug.
jmo,
.
 

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Could have NGK or Denso plugs from the factory. And I'd set the gap at the minimum spec. I use .028" If you have a weak battery or charging system, the narrower gap is just that much easier for the spark to jump. The narrow gap fixed my 1100 hard starting issues.

36
SPARK PLUG (X27EPR-U9) (DENSO)

98069-59926


Also possible the fuel pump is not running and it's able to gravity feed enough fuel for lower speeds. Or the fuel cut relay is bad. Easy to test, under the right side cover there is a relay with 3 wires, black, black-blue, and yellow blue. Unplug the relay, make a jumper and jump black to black-blue in the harness plug, tape it up. When you turn the key on, the pump should click rapidly for a second or two, slow and stop as the floats cut off flow. If you hear the pump do that, the pump should be OK. Take it for a ride, see if it is still has a problem. Note the fuel cut relay is there to stop the pump if you crash and the motor dies... ride at your own risk.
 

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Discussion Starter · #11 · (Edited)
I plan to replace the carb boots already, for under 3 dollars a plug that seems like such a cheap thing to just replace anyway.
Honda OEM plugs ARE NGK, iridium plugs would be the same NGK number as OEM.
1999 Honda VT750CD2 A CYLINDER HEAD (RR.) | Ron Ayers
#36 spark plug.
jmo,
.
Already ran into an issue with spark plugs. My toolbox is missing the spark plug tool so I figured no big deal, I'll look up the hex size I need and found it should be 18mm. I got a new 18mm spark plug socket from the store and realized it doesn't bite at all. I put a 17mm deep well in there and it has a soft bite on the threads, but not tight enough to safely put torque on so I'm thinking it's either a 16mm or if it's somehow standard 5/8" hex. I'll probably buy a few and see which one fits so I can take a look at plug condition.
 

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Discussion Starter · #12 ·
So I got a 5/8" spark plug socket and it fit. I took out the easiest of the 4 (rear left) and this is my finding in the pictures. They're obviously used, but the plug gap is about 30 mils (it was tight, 29 mils passed easily). Worth it to get them replaced. Also found out that even though these have what look like threads on the end, I just pulled the plug off like you would on a lawn mower without an issue so it wasn't threaded on there. Wondering if that could cause a lot of extra resistance leading to bad spark. Also these are "Champion 588" spark plugs. Plan to order new plugs.
 

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That's a pretty normal looking plug, It's not an Iridium (the expensive ones) I would throw the Champion plugs away and get NGK or Denso. My experience is Hondas just don't like Champion plugs. cars or motorcycles. I believe Champion also still uses a cut thread instead of a smoother machine rolled thread like NGK, some mechanics say the cut threads are harder on aluminum heads.
 
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Discussion Starter · #15 ·
That's a pretty normal looking plug, It's not an Iridium (the expensive ones) I would throw the Champion plugs away and get NGK or Denso. My experience is Hondas just don't like Champion plugs. cars or motorcycles. I believe Champion also still uses a cut thread instead of a smoother machine rolled thread like NGK, some mechanics say the cut threads are harder on aluminum heads.
I figured that too, I thought maybe a hair rich but another friend of mine said they looked fine. Just ordered some new plugs anyway and they're so cheap it's good insurance. Also got carb boots too since mine are over 10 years old and from youtubing it seems to be a common thing that becomes hard as a rock over time.

The iridium plugs seem to be an aluminum block thing in general because a quick search for my current truck is they use iridium's now on LQ83 GM engines which are AL blocks and heads. My old LM7 was a cast iron LS and misfired a lot iridium plugs. This could also just be a big coincidence. Anyway shipping says last week of July so we'll have to wait and see on this one. In the meantime I'm going to test the fuel pump as well.
 

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Discussion Starter · #16 ·
That's a pretty normal looking plug, It's not an Iridium (the expensive ones) I would throw the Champion plugs away and get NGK or Denso. My experience is Hondas just don't like Champion plugs. cars or motorcycles. I believe Champion also still uses a cut thread instead of a smoother machine rolled thread like NGK, some mechanics say the cut threads are harder on aluminum heads.
Really bad news. I went to ride today and as soon as I left my house the bike stalled on me about 10 feet from my driveway.

I put the plug back in and the boot back on (slipped it on like I slipped it off of there). No idea what's happened in the meantime. I did a few small pulls in my driveway and could feel the bike losing it by the time I was fully leaving the clutch. Also in neutral it tried to stall out a few times at higher revs. It never did anything like this since the last time I rode.

I also put highway bars on the bike too, but that was just mounting it to the foot pegs and frame.
 

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Going to have to pull the carbs and check the diaphragms... though they should have been checked/replaced if the carbs were rebuilt.
 

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Discussion Starter · #18 ·
Going to have to pull the carbs and check the diaphragms... though they should have been checked/replaced if the carbs were rebuilt.
How would that have changed so much since just checking a plug? I may check tomorrow if the plug wasn't torqued in enough. Maybe just lost compression and essentially ran on 1 cylinder?

Also when I put the highway bars on, I had to loosen the headpipes. Could something have gotten messed up somehow?
 

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Both are possible. as well as a possibly bad plug wire or any number of things, hard to see from here...
 

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Discussion Starter · #20 ·
Both are possible. as well as a possibly bad plug wire or any number of things, hard to see from here...
I just went back out and took out the spark plug and reinstalled it with more pressure this time. I really need a torque wrench though because I don't want to break the threads. Plugged the wire back up and it ran fine. Did my hill test again in 2nd gear and got stuttering at the high end and then went and did some figure 8 and u turn practice at a local HS parking lot. When I decided to leave and come back home, my bike started sputtering (almost sounded like some random backfires) and I could smell a slight burning smell. The stuttering continued and I hardly made it up the hill to my neighborhood. Finally got to the top and it quit on me. Held the starter for a good 10 seconds and thankfully restarted hardly and basically coasted home downhill in 2nd.

Possible the spark plug vibrated lose because I just didn't torque it enough?
 
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