72 CB350f power problems

4614 Views 22 Replies 3 Participants Last post by CB750F, Sep 13, 2007

xbrainchild

Discussion Starter · Aug 25, 2007

Hey guys. I'm semi-new to owning a real motorcycle. I bought a 72 cb350f off of craigslist for about 300 bucks. It ran, but needed some things.

I changed the oil, took the carbs apart and cleaned them very well, added a fuel filter, removed some rust from the tank, and did a few other minor things.

Every morning when I go outside to work on it, it starts up pretty nicely (I have to jump it cause the battery is shot, but it starts like a champ.) I can ride it about a half mile or so getting pretty good power, and then it just seems to die down. It'll stall out and then be really hard to start back up again, if I do get it started it doesn't even have enough power to accelerate in 1st gear. I was told it may be the Coils since it is losing power when it heats up. I replaced the coils with ones I bought off of ebay (the seller said they were tested and worked fine) but it is still having the same problems. Does anyone have ANY idea how to fix this?

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CB750F

· #2 · Aug 26, 2007

One thing to check is the valve lash. The engine starts ok cold but hard to start hot is one of the signs of too tight valve clearance. The engine gets hot, the metal expands in the valves and if there isn't enough clearance it can hold the valve slightly open and loose compression, killing performance and making it hard to start when hot. It don't cost a dime to check that other than buying feeler gauges.

I would replace the points and condensers first before going into anything radical also if the valve lash is ok. You may need to do a real good tune up on it.

xbrainchild

Discussion Starter · #3 · Aug 26, 2007

Okay, how exactly do I check the Valve lash and how do I know if its wrong? And what do I do to fix it? (I'm new to this :\)

xbrainchild

Discussion Starter · #4 · Aug 26, 2007

Also, will this condenser:

cmsnl.com/products/condenser_30280292672

and these points:

cmsnl.com/products/points-assy_30200286004

work with the CB350 Four?

CB750F

· #5 · Aug 27, 2007

If it says it will work for the CB350 4 then they will work for it. Generally all the CB point sets are the same just the backing plate changes. Pick up a shop manual. It will tell you how to set the valves and the points. Do it while the bike is cold for the valves,like after it sits overnight. Even if it has ran in the past couple hours it will give you a false reading.

xbrainchild

Discussion Starter · #6 · Sep 4, 2007

Alright. I haven't gotten any time within the past couple weeks to work on my baby but now I'm back and I've got 2 days off in a row to get her running. So I have one question, should I replace the condenser and points before doing the valve lash?

CB750F

· #7 · Sep 4, 2007

Do the valves first, that don't cost a dime.

xbrainchild

Discussion Starter · #8 · Sep 4, 2007

Also, I think the power loss may be coming from the piston rings being worn? When I turn on my bike it has a lot of blue smoke coming out the back, isn't that a sign that the rings are shot?

If they are, I'm gonna replace them, but I don't know what to buy. Will rings for a normal CB twin work with the CB350 Four?

xbrainchild

Discussion Starter · #9 · Sep 4, 2007

WELL! After about 5 hours of work today, my bike finally runs like a champ. I was cruising all over the place with it, fun times. I need a serious carb rebuild though, 3 out of 4 of them pour gas out of the bleed hoses while the gas is on (running or not) so I've gotta fix that.

CB750F

· #10 · Sep 5, 2007

What all did you do with it? The rings off a CB twin are different than your 4 cylinder one.

xbrainchild

Discussion Starter · #11 · Sep 5, 2007

Well I don't think I need new rings because I'm getting amazing power out of it now. Feels absolutely perfect. I replaced the coils and I (prepare for me being an idiot) when cleaning out the fuel system I forgot to check the pet****. Opened that bad boy up and it was filled with the thickest gooiest **** ever. It looked like a mixture between molten lava and quicksand. So gross. Cleaned that all up and now she runs like a champ.

One problem though, 3 out of 4 of the carbs leak out the bleeder hoses. Not so good. I'm probably gonna have to rebuild them, unless you have any suggestions as to why they would be leaking? I checked the bleed screws they are all tight they just leak for some reason.

And also I'm gonna need a new gas tank, mines rusted as ****. They are realllly hard to find though, especially for the 350f's.

CB750F

· #12 · Sep 5, 2007

Check your other post. Might want to look into this stuff called Kreem or hunt around on Ebay for a tank.

xbrainchild

Discussion Starter · #13 · Sep 6, 2007

Just got a good tank off ebay for 36 bucks. Not sure how I pulled that off considering the last one I saw on ebay went for 230. Strange.

Guy

· #14 · Sep 7, 2007

Check the carb floats on one of the leaky carbs. The lever may be rusted or sticking, or the float may be bad. In either case, I'd re-build the carbs and replace the floats just to get them up to spec.

CB750F

· #15 · Sep 7, 2007

xbrainchild said:
Just got a good tank off ebay for 36 bucks. Not sure how I pulled that off considering the last one I saw on ebay went for 230. Strange.

SCORE! I ended up paying $25 for a perfect used seat for my 750 couple months ago on there and like you, I don't know how I pulled that one off. Probably because the tailpiece looked like ****.

xbrainchild

Discussion Starter · #16 · Sep 11, 2007

Yeah seriously! I just watched 2 more tanks go for over 200 yet somehow I snagged mine for 36 bucks. Deal.

I also got a brand new set of mirrors and the stock tailbar (The moron before me put some assaninely huge sissy bar on the thing, looked SO ugly.)

But yeah, now that she runs I'm gonna try to restore her as much as possible. I want her to run and LOOK like brand new.

It's gonna be a looooong rough road.

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CB750F

· #17 · Sep 11, 2007

One of these days I'm going to do a bike up all 70's style with every goofball item you could get out of the K&L or JC Whitney catalog back in the day. Like the humoungous sissy bar, the luggage rack for the back, engine guards that stuck way out on the front and doubled as highway pegs and possibly a huge Vetter fairing with an 8 track player and an old school Kerker pipe. Then I'll cover it it gold paint with the biggest metalflake I can find that will shoot out of a gun. The CB750 I bought for parts had the huge engine guard/highway peg set up and a zillion lights all run by toggle switches. Shoulda kept that stuff.

xbrainchild

Discussion Starter · #18 · Sep 11, 2007

Jesus christ. So I just got a call from the place that was doing my so called 100$ carb rebuild and cleaning. They said the casing of one of the main jets in my carb would need to be replaced and that its a 300 dollar job. Screw that I'm doing it myself. I'm going down there to buy an extra carb body now for 50 bucks and I'm rebuilding the things by myself.

xbrainchild

Discussion Starter · #19 · Sep 13, 2007

I need to buy 4 new floats. Where can I get them cheap?

CB750F

· #20 · Sep 13, 2007

Give www.oldbikebarn.com a try for those. If not start searching the net.

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