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Author Topic: 71 cb750 new engine build  (Read 18226 times)

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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #25 on: August 20, 2011, 05:28:26 PM »
Im so confused. What is the definition of balancing and what the machine shops do?
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #26 on: September 20, 2011, 11:39:04 PM »
Ok so I got the engine together and in the frame using the cycle x git kit. Just did a compression test and tested 150psi across all cylinders. Is that good or is it supposed to ne higher? Also the compression tester is from harbor freight so it could be off a bit. Tomorrow I will mount the carbs and attempt to start her up
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #27 on: September 24, 2011, 10:59:44 AM »
Got to ride the bike last night for the first time. It rode awesome for a while then all of a sudden it looses all performance and feels like it is over heating. It has pod filters and a fairly open 4-1 exhaust. The carbs have 140 mains and the needle lowered 1 clip to clip 2. Im thinking it is still running lean but has 140to jets. Any suggestions?
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Online MRieck

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Re: 71 cb750 new engine build
« Reply #28 on: September 24, 2011, 01:28:06 PM »
140 main is very large. Check your plugs.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #29 on: September 24, 2011, 01:40:07 PM »
Checked the plugs and 3u of them appear fine but cylinder 1 appears not to be firing. So possibly an ignition problem?
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Re: 71 cb750 new engine build
« Reply #30 on: September 24, 2011, 04:51:24 PM »
Quote from: orkid1989 on September 24, 2011, 01:40:07 PM
Checked the plugs and 3u of them appear fine but cylinder 1 appears not to be firing. So possibly an ignition problem?
Not to be a smart a$$ but it is either fuel or ignition. Is the plug wet? Go through all the checks before taking it for an extended ride. It is BAD to have a cylinder filling with fuel with no spark.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #31 on: September 24, 2011, 05:04:16 PM »
Quote from: MRieck on September 24, 2011, 04:51:24 PM
Quote from: orkid1989 on September 24, 2011, 01:40:07 PM
Checked the plugs and 3u of them appear fine but cylinder 1 appears not to be firing. So possibly an ignition problem?
Not to be a smart a$$ but it is either fuel or ignition. Is the plug wet? Go through all the checks before taking it for an extended ride. It is BAD to have a cylinder filling with fuel with no spark.
No it looked like it was brand new out of the box.
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Re: 71 cb750 new engine build
« Reply #32 on: September 24, 2011, 05:20:18 PM »
Quote from: orkid1989 on September 24, 2011, 05:04:16 PM
Quote from: MRieck on September 24, 2011, 04:51:24 PM
Quote from: orkid1989 on September 24, 2011, 01:40:07 PM
Checked the plugs and 3u of them appear fine but cylinder 1 appears not to be firing. So possibly an ignition problem?
Not to be a smart a$$ but it is either fuel or ignition. Is the plug wet? Go through all the checks before taking it for an extended ride. It is BAD to have a cylinder filling with fuel with no spark.
No it looked like it was brand new out of the box.
I would say a fuel problem. Are they CR's?
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #33 on: September 24, 2011, 05:24:14 PM »
Quote from: MRieck on September 24, 2011, 05:20:18 PM
Quote from: orkid1989 on September 24, 2011, 05:04:16 PM
Quote from: MRieck on September 24, 2011, 04:51:24 PM
Quote from: orkid1989 on September 24, 2011, 01:40:07 PM
Checked the plugs and 3u of them appear fine but cylinder 1 appears not to be firing. So possibly an ignition problem?
Not to be a smart a$$ but it is either fuel or ignition. Is the plug wet? Go through all the checks before taking it for an extended ride. It is BAD to have a cylinder filling with fuel with no spark.
No it looked like it was brand new out of the box.
I would say a fuel problem. Are they CR's?
I wish. No they are the original stock carbs.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #34 on: September 26, 2011, 02:12:00 PM »
think i might have figured out one problem. my coils are overheating plus they are below 3ohm with no modification so i bought new 5ohm dyna coils and the copper core wires last night. I'm going to put them on the bike and see what happens. also i bought 1/4" clear fuel line so i can make sure that i am getting good fuel flow and the fuel shutoff valve isn't getting clogged
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #35 on: September 30, 2011, 04:20:56 PM »
got the coils, wires, plugs, and coil wire modification installed. also installed a removable baffle to help with the flow in this crappy exhaust. fired it up and it is finally running rich! also all cylinders are firing like they should. now i just need to go a jet size or two down to get the A/F just right then sync the carbs. i do have a question though. i was wondering what will cause the motor to rev up and down at idle when not touching the throttle?
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #36 on: September 30, 2011, 07:07:43 PM »
slight problem. when i try to use the electric starter on the bike it will start to turn over the motor then it will just start spinning without the motor turning over. stripped gear maybe? what would happen if the starter clutch goes out?
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Re: 71 cb750 new engine build
« Reply #37 on: September 30, 2011, 07:21:40 PM »
Quote from: orkid1989 on September 30, 2011, 07:07:43 PM
slight problem. when i try to use the electric starter on the bike it will start to turn over the motor then it will just start spinning without the motor turning over. stripped gear maybe? what would happen if the starter clutch goes out?
The rotor mounting bolt is not tight enough.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #38 on: September 30, 2011, 07:30:53 PM »
Quote from: MRieck on September 30, 2011, 07:21:40 PM
Quote from: orkid1989 on September 30, 2011, 07:07:43 PM
slight problem. when i try to use the electric starter on the bike it will start to turn over the motor then it will just start spinning without the motor turning over. stripped gear maybe? what would happen if the starter clutch goes out?
The rotor mounting bolt is not tight enough.
are you talking about the large bolt that mounts the stator? Presses it to the crankshaft
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #39 on: October 01, 2011, 02:16:52 PM »
i figured it out. got the carbs synced up this morning and now the bike runs AWESOME! rode it on the highway. now all i need to do is read the plugs and make sure everything is all good.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #40 on: October 01, 2011, 07:12:31 PM »
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing. any ideas? i read something about having problems with side wind on pod filters. any chance that has something to do with it?
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Offline Sam Green Racing

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Re: 71 cb750 new engine build
« Reply #41 on: October 02, 2011, 02:57:44 AM »
Perhaps time for that plug chop.

Sam. ;)
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Re: 71 cb750 new engine build
« Reply #42 on: October 02, 2011, 06:27:24 AM »
Quote from: orkid1989 on October 01, 2011, 07:12:31 PM
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing. any ideas? i read something about having problems with side wind on pod filters. any chance that has something to do with it?
I highly doubt it. Like Sam said I'd check the plugs and take it from there.
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #43 on: October 02, 2011, 06:51:55 AM »
Checked the plugs and 1 and 4 are just a little bit lean while 2 and 3 look like they are rich. Possibly float level height is off? They are all synced up and have new jets from jetsrus.com
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #44 on: October 04, 2011, 09:14:41 PM »
ok now i have a problem. i just checked the compression across the cylinders and 1 and 2 read 150psi but 3 reads 120psi and 4 reads 90psi. i read about an old trick where you put a small amount of oil in the cylinders and check the compression and if it goes up its the rings so i did it and the compression went up. the only problem is that i have maybe an hour or so of run time and it hasnt overheated. its got a bit warm but not overheated. i was wondering if anyone had any ideas? just cant see why rings could go that bad that fast
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Offline scunny

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Re: 71 cb750 new engine build
« Reply #45 on: October 05, 2011, 12:01:43 AM »
Quote from: orkid1989 on October 01, 2011, 07:12:31 PM
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing.

did you bed the motor in under load first or just hit the throttle ?
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #46 on: October 05, 2011, 09:04:49 AM »
Quote from: scunny on October 05, 2011, 12:01:43 AM
Quote from: orkid1989 on October 01, 2011, 07:12:31 PM
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing.

did you bed the motor in under load first or just hit the throttle ?
well I blipped the throttle while syncing the carbs. Then road it around the block. Then hit the highway for break in
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #47 on: October 16, 2011, 09:05:39 PM »
Everything is going well and all of a sudden somehow managed to snap a new headstud... guess now I have to buy a whole other set. Along with possibly another head gasket.  :'(
« Last Edit: October 19, 2011, 04:06:33 PM by orkid1989 »
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Offline Retro Rocket

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Re: 71 cb750 new engine build
« Reply #48 on: October 16, 2011, 10:19:56 PM »
Quote from: orkid1989 on October 05, 2011, 09:04:49 AM
Quote from: scunny on October 05, 2011, 12:01:43 AM
Quote from: orkid1989 on October 01, 2011, 07:12:31 PM
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing.

did you bed the motor in under load first or just hit the throttle ?
well I blipped the throttle while syncing the carbs. Then road it around the block. Then hit the highway for break in

Well pods won't help.... And you need to vary the loads on the engine for proper running in, the highway is not ideal....
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Offline orkid1989

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Re: 71 cb750 new engine build
« Reply #49 on: October 19, 2011, 04:08:34 PM »
Quote from: Retro Rocket on October 16, 2011, 10:19:56 PM
Quote from: orkid1989 on October 05, 2011, 09:04:49 AM
Quote from: scunny on October 05, 2011, 12:01:43 AM
Quote from: orkid1989 on October 01, 2011, 07:12:31 PM
my bike has all the power i want up untill i get in the 80-90 mph range then it has nothing.

did you bed the motor in under load first or just hit the throttle ?
well I blipped the throttle while syncing the carbs. Then road it around the block. Then hit the highway for break in

Well pods won't help.... And you need to vary the loads on the engine for proper running in, the highway is not ideal....
cool thanks for the tip. think ill have to take it out in the country or something to try breaking it in. around where i am at their is mostly either stop and go traffic and the highway
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