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Lost 20mph on my Takegawa 88 motor

3.5K views 39 replies 13 participants last post by  EddieNewYork  
#1 ·
I finished building my bike and took it for a test ride today. For some reason, it felt like a stock motor. This motor use to do 50mph easily, but today it topped out at 30mph. :confused:



The changes I made were...



Wheels from 10" to 8"

Gearing from 15/37 to 15/33 (ran this through honda50.com's gear ratio calc and the numbers are near identical)

Carb from YSN to a Shengway (see below for specs)

Manifold from Kamikaze to TB

Adjusted the valves



Numbers rounded off for easy reading...



The Shengway is 20mm on the manifold side, 29mm on the intake side, and the slide is 17mm.



The YSN is 22mm on the manifold side, 29mm on the intake side, and the slide is 18mm.



Any ideas? Is it possible to lose 20mph because I changed carbs?



Build thread here.



Image
 

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#5 ·
supernes550 said:
bike looks good eddie.

you're right about that fender. it's tiny. maybe try looking at a mid 90s z50 fender.



my guess is that the wheels are actually heavier than the skinnier crf stockers.

is that mph reading from the vapor or gps?


Thanks Ernesto. It's reading off my vapor, but I was going by feel mostly. Cars were passing me left and right, lol. :irked:
 
#6 ·
What ernesto said. How did you measure speed and how did you go about the error correction on the speedo? Moving down from 10" to 8" tires, your speedo would read much faster then it did on 10" tires.



Start there to see if your speedo is calibrated correctly unless you were using GPS.



Why did you switch carbs to begin with if the one you had was working?



Put the old carb back on and see where you stand so you can start troubleshooting.
 
#7 ·
Z said:
What ernesto said. How did you measure speed and how did you go about the error correction on the speedo? Moving down from 10" to 8" tires, your speedo would read much faster then it did on 10" tires.



Start there to see if your speedo is calibrated correctly unless you were using GPS.



Why did you switch carbs to begin with if the one you had was working?



Put the old carb back on and see where you stand so you can start troubleshooting.


Thanks Dan, I entered new values into the speedo, but I don't think it's the speedo. I was going more by feel. :D



I switched carbs because I just thought my old carb was tired and wanted to try a new shengway carb, lol.



Yeah, that's what I plan on doing first. I'll report back my findings soon.
 
#8 ·
I would try to tune your carb a little bit better. I had a similar problem at one point. The bike ran fine but if I stayed wot too long I would get a stutter. I dropped my jetting a bit leaner and the bike gained about 5 mph. Now it runs perfect and is more than enough to pull me around until I can go bigger. ;) What RPM are you revving to in 3rd?
 
#10 ·
s_10onbagz said:
I would try to tune your carb a little bit better. I had a similar problem at one point. The bike ran fine but if I stayed wot too long I would get a stutter. I dropped my jetting a bit leaner and the bike gained about 5 mph. Now it runs perfect and is more than enough to pull me around until I can go bigger. ;) What RPM are you revving to in 3rd?


Funny you mention that, because when I was WOT it started pulsing every 5 seconds or so. I didn't get the RPM's yet. I forgot to reset my vapor speedo max reading screen, doh!



What RPM's do 88 motors rev to?
 
#11 ·
Z50King said:
gearing it up may have been your problem. what size tires were you running on your 10 inch rims, and what size tires are you running now?



and what road is that? sorta looks like gmr, but i dont think it is


I was running TT91 90/90/10s and I'm running Heidenau k75 3.5x8.



That's the road going up to the Griffith Observatory. :)
 
#13 ·
I rev to around 9000-9500 rpm when I am doing a top speed run. I try to cruise at around 7000rpm. I have hit over 10k rpm, but I try to avoid it. What jets are you using?
 
#17 ·
Z50King said:
15/33 is a very tall gearing. does it feel like its revving as high as it used to?



as for the tires, measure the biggest diameter, i never understood how they measured those 8 inch tires at 3.5 inchs



the old tires should have had a diameter of near 16 inches (?)


Yeah, it feels like it revs normally, but I lost a lot of torque. I'll take some measurements tonight and report back.
 
#21 ·
Well, you've done three things that could affect the motor's power.



1. Adjusted the valves

2. Replaced the manifold

3. Replaced the carb



So...it's probably one of those three things . Validate again the valves. I run em .003 on the intake and .004 on the exhaust.



You could have a leak causing a lean condition...once you get up in the rpms it could be sucking air somewhere. You can always put the old carb and intake on and see what happens.
 
#22 ·
fatcaaat said:
Well, you've done three things that could affect the motor's power.



1. Adjusted the valves

2. Replaced the manifold

3. Replaced the carb



So...it's probably one of those three things . Validate again the valves. I run em .003 on the intake and .004 on the exhaust.



You could have a leak causing a lean condition...once you get up in the rpms it could be sucking air somewhere. You can always put the old carb and intake on and see what happens.


Thanks fatcaaat, I'll check and do those things and report back.
 
#25 ·
EddieNewYork said:
Really?? I'm 99% positive 8" Z wheel+tires are smaller in diameter then the CRF wheel+tires the last time I measured.


Well, yes the wheels are smaller. But the OD of the tires is bigger on the Z. I'm sure that you can find a small tire for the Z and a large one for the CRF. This is somewhat more unbelievable, but my Z50R wheels are lighter than my CRF wheels. I don't blame you if you don't believe me, I find it hard to believe.
 
#26 ·
arlindsay1992 said:
Well, yes the wheels are smaller. But the OD of the tires is bigger on the Z. I'm sure that you can find a small tire for the Z and a large one for the CRF. This is somewhat more unbelievable, but my Z50R wheels are lighter than my CRF wheels. I don't blame you if you don't believe me, I find it hard to believe.


It's not that I don't believe you, but I remember comparing the 8" Z wheels with the 3.5x8 tires on next to the crf 90/90/10 and the Z was smaller. However, you may be right if we're comparing stock crf knobbies.