Author Topic: Questions for you 750 guys  (Read 1592 times)

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Offline Flying J

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Questions for you 750 guys
« on: September 05, 2008, 12:34:35 PM »
Question 1: I was riding down the freeway and the engine started to cut out. I changed to res but it still was surging and sputtering so i got off the freeway and shut it down for a minute. It eventualy started up. i got back on the freeway and it died in 2 more exits. I sat on the side of the free way for a few minutes and stared it back up road surface streets home and it was fine. Is that normal when you switch to reserve or is this posibly an overheating problem. I was running in 6200 rpm range.

Question2: at about 6000 rms in 5th gear when i accelerate it looses power for a second then accelerates. What can i do to fix this. Is it a jetting problem

Question 3: I bought a 750F motor and a front comstar with rotors for $175. The engine turns and is missing a few covers. Did i get taken?

Question 4: Is there anywhere to get stock piston rings for a F motor?
« Last Edit: September 05, 2008, 12:53:37 PM by ffjmoore »

Offline dustyc

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Re: Questions for you 750 guys
« Reply #1 on: September 05, 2008, 12:54:59 PM »
Question 1: I was riding down the freeway and the engine started to cut out. I changed to res but it still was surging and sputtering so i got off the freeway and shut it down for a minute. It eventualy started up. i got back on the freeway and it died in 2 more exits. I sat on the side of the free way for a few minutes and stared it back up road surface streets home and it was fine. Is that normal when you switch to reserve or is this posibly an overheating problem. I was running in 6200 rpm range.

Question2: at about 6000 rms in 5th gear when i accelerate it looses power for a second then accelerates. What can i do to fix this. Is it a jetting problem

Question 3: I bought a 750F motor and a front comstar with rotors for $175. The engine turns and is missing a few covers. Did i get taken?

That's not a normal thing in reserve.  The reserve passages that may be gummed up and not letting enough gas through to fill up the carbs.

I don't think you were taken with that deal.  It really depends on the condition of the engine. 

If it was abused and the crank rattles around, has no compression and burned valves, probably not the best deal.

If it was well loved, has low miles, great compression and no issues except a missing cover, it would be a great deal to me.

You're going at it blind, so I would try to pay as little as possible, like when someone says a bike ran great before they parked it, but it won't run now, you have to pay as if you're buying the worst case scenario.  But that sounds pretty fair.  There isn't an absolute set value, so it comes down to what you and the seller think is a good deal for each of you.

1977 CB750

Offline andy750

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Re: Questions for you 750 guys
« Reply #2 on: September 05, 2008, 01:15:08 PM »
Question 1: I was riding down the freeway and the engine started to cut out. I changed to res but it still was surging and sputtering so i got off the freeway and shut it down for a minute. It eventualy started up. i got back on the freeway and it died in 2 more exits. I sat on the side of the free way for a few minutes and stared it back up road surface streets home and it was fine. Is that normal when you switch to reserve or is this posibly an overheating problem. I was running in 6200 rpm range.

Question2: at about 6000 rms in 5th gear when i accelerate it looses power for a second then accelerates. What can i do to fix this. Is it a jetting problem


Should be no problem running in the 6000 rpm range for extended periods. And should accelerate cleanly at this rpm - at least my K2 does. Id agree with Dusty that you likely have a fuel delivery issue somewhere...id check that out first. Usually before I switch to reserve I get a "cough", loss of power, which is then resolved as soon as I switch to reserve.

Good luck

Andy

Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline Johnie

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Re: Questions for you 750 guys
« Reply #3 on: September 05, 2008, 01:48:06 PM »
Another thought for you, be sure your gas tank vent is not plugged creating a vacuum in the tank.  If this happens again, crack the gas cap and see if she run normal.
1970 CB750K0 - Candy Ruby Red
1973 CB750K3 - Candy Bacchus Olive or Sunflake Orange
1970 Chevy Chevelle SS396 - Cortez Silver
1976 GL1000 Sulphur Yellow

Oshkosh, WI  USA

Offline MT_CB750K8

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Re: Questions for you 750 guys
« Reply #4 on: September 05, 2008, 02:12:39 PM »
+1 on the tank vent my ZR550 acted the same way when on the highway for extended periods.  Thing that gives it away is if you open the cap and you hear air rush in.  My K8 has 18/48 sprockets w/ 530 chain and in 5th not great acceleration from 70+ but no bog.
Present Rides: 1978 CB750K, 2002 KLR650
Past Rides:  1975 GL1000, 1991 ZR550, 1999 CR125, 2004 KDX220

NWrider

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Re: Questions for you 750 guys
« Reply #5 on: September 05, 2008, 09:41:48 PM »
Stock CB745F rings are available from Service Honda. I recently purchased a set of 4. They were about 27.50 per piston.
NWR

Offline neil10

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Re: Questions for you 750 guys
« Reply #6 on: September 05, 2008, 10:25:22 PM »
look at fuel lines see if they are close to engine. To close will cause gas to  become gas. Real gas

Offline Flying J

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Re: Questions for you 750 guys
« Reply #7 on: September 06, 2008, 09:01:04 AM »
Fuel line is far enough away, but good idea i didnt think of that. I sure that it was that it ran out and maybey a combination of that and my pet cock might be a little slow flowing.

Offline Flying J

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Re: Questions for you 750 guys
« Reply #8 on: September 11, 2008, 12:38:18 AM »
I think somewhere around 7500 rpms my engine is sucking fuel faster then the carbs can send. On a hour long ride today the bike was fine but then i pinned it to see how fast it would go (111mph) it then cut out. I pulled to the sholder and coasted for a ways and then popped the clutch in first. It started, reved it a few times and then back on the road fine. Is it the carbs or is my petcock not flowing fast enough?

Offline dustyc

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Re: Questions for you 750 guys
« Reply #9 on: September 11, 2008, 10:05:42 AM »
I'd look at the petcock first.  If it's crapped up, that's probably the main cause.  Of course, if you haven't been into your carbs and the petcock has junk in it, your carbs probably need cleaned too. 

If the petcock is clean, check your float height.  PO could have messed them up.
1977 CB750

Offline Flying J

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Re: Questions for you 750 guys
« Reply #10 on: September 11, 2008, 10:38:59 AM »
When i bougt the bike a month ago i strippedthe carbs all the way down and cleanded them. I also adjusted the floats to specs and had it all synced. What am i looking for on the petcock? Is it the tube in the tank that is slowing it or is it inside the petcock that might be the problem?

Offline dustyc

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Re: Questions for you 750 guys
« Reply #11 on: September 11, 2008, 11:12:11 AM »
If it's a later bike, it has an internal filter screen "sock" you'll need to make sure is clean.  If it's earlier, it has a screen in the bowl and check the reserve passages too.  And run a pipe cleaner through the normal(not reserve) intake pipe just to make sure no bugs, etc. floated in.

I'd just take it as far apart as you can and clean everything you can.

If that doesn't do it, go back into your carbs and make sure you didn't put the floats in upside down.
1977 CB750

rhos1355

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Re: Questions for you 750 guys
« Reply #12 on: September 11, 2008, 11:51:35 AM »
I might just be pissing in the wind but I've just had an idea; could it be your ignition switch? Just read an alarming post on the forum about ignition switches going awol and switching the whole bike off?

http://forums.sohc4.net/index.php?topic=40489.0;topicseen#top

Offline Flying J

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Re: Questions for you 750 guys
« Reply #13 on: September 11, 2008, 04:57:08 PM »
I think my bike just doesnt like going 90+ mph. Maybe ill rebuild the petcock.