1982 CB750F...Better Devil

pidjones

Over 1,000 Posts
A '76 GL should make a nice platform. I'd like to see one turned into a lightweight four-wheeler. Maybe even an open-wheel. Plenty of cafe racer GLs. Not many choppers, but the ones I've seen looked awkward. Many try going single-carb. Many go back to four because Honda knew what they were doing.

Or, keep the rear drive and change out the engine to an in-line 3 or 4 like the early Ace and Indians or the present Rocket 3. Would a Suzuki 3 cylinder from a Chevy Sprint do it?
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
It does mate, feels great. I'm going to try the official route getting this bike on the road (as opposed to the loophole method I did with Rhonda) - hopefully I can get an appointment for a mechanical inspection (needed here in Quebec if your ride has been off the road longer than a year) and then I'm off to the races.

Adjusted the clutch today which made shifting a lot easier, but a cop sailed past and put the kibosh on me taking the thing round the block again. Have to say the ergonomics one this bike are great - the saddle, the bars...damn it fits me well.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Well, we got her out the gate but there's a stumble at the first hurdle. No leaks, gas flow seems to be ok, battery charged. Was running on all four but now it's only firing on two cylinders, 1 & 2.

Idle is woeful. Even with the choke fully engaged the engine really struggles, and dies. Really feels like it's not getting gas. I played with the throttle screw on the carb to increase the rpm to the point where the engine doesn't stall, and also turned out the mixture screws half a turn. Any ideas?
 

Maritime

Over 10,000 Posts
Don't overlook the chance that crap was sequestered somewhere in the fuel path and has now contaminated once-clean carbs.
This. I cleaned the bejeebus out of my GL carbs, installed all new lines and filters and still found crap in the bowels when taking them off to find my fuel issue.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Don't overlook the chance that crap was sequestered somewhere in the fuel path and has now contaminated once-clean carbs.
The more I think about it the more I'm inclined to think you're right. Of course I won't know for sure until I have a look in the carbs, bowls and filters but the only thing that really changed between a smooth running bike (with an auxiliary tank attached) and a rough bugger was the installation of the gas tank.

I did a lot of work on repairing large dents on the tank, and used all manner of steps and chemicals (including MEK, Metal Rescue, and a bunch of coarse chain to knock off rust) to clean out the insides. The dent in the tank was on the top however, and so looking inside the tank I could not tell how that dent looked from the inside. Now, I'm thinking, it may not have looked so good.

Don't want to get too far ahead of myself but thinking maybe some Caswell Dragons Blood is in my near future. Still, one step at a time.
 

chickenStripCharlie

Been Around the Block
Did you not install any kind of filter?

After realizing what a pain 4 carbs are, and not wishing to do it again any time soon, i put the strainer filter on the petcock and an inline fuel filter downstream a bit.

The bike looks BEAUTIFUL! Really well put together. Just great.
The seat came out perfect as well. Is it vinyl? It looks like leather used in car seats not viny.

Just awesome.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Thanks Charlie, I appreciate that. Definitely installed fuel filters - there's one on the petcock and another inline filter on the fuel line. Pulled the tank and carbs - definitely some rust in there. Both in the tank and the bowls - and no doubt the carbs and jets too. So took them apart and nearly done giving them another thorough clean. Didn't pull the bank apart this time, but did finagle a tool to get to the air cut-off valve covers. Came up with a little trick to re-install them - I'll post up some pics soon.

So yeah, looks like the dent in the tank had rusted out and that was dumping crap into the carbs. Cut the inline filter up and strangely didn't find any rust in there at all, which leads me to wonder if there are inline fuel filters and then there are inline fuel filters. Maybe mine were shite - should I be looking for a brand in particular? Mine were Bike Master I think.

Drained all the gas out of the tank, and used my new vacuum brake bleeder pump to suck up the remaining gas and crap out. I'll clean it up as best I can, sling some coarse chain in there and knock off as much rust again as I can. Then I'll coat it with some Caswell Dragons Blood liner. Gonna order some now.

By the way, the seat is a marine grade vinyl. Looks and feels just like leather, but weatherproof and really strong.


 

chickenStripCharlie

Been Around the Block
Damn, man. That sucks after all that time getting everything buttoned up.

That is really strange given your inline filter. I would expect a cheap one to have cracked and leaked before it remained tight but let flakes of rust through. Doesnt add up.

Wonder if there is a chance the line downstream of the filter was contaminated before install?
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Yeah, it’s all good, I mean shit it could be better, but I’ve been through cb750 carbs so many times now that I’m ok with it. Rather get it right eventually even if it means a bunch of wrong getting there.

I thought the same thing, how in the hell does a decent piece of rust (grain of sand-ish) get through two filters? Beats me, but it did. A bunch of them.


Sent from my iPhone using DO THE TON
 

pidjones

Over 1,000 Posts
To get a good llok at your tank roof, buy a cheap boroscope/endoscope camera (~$12). Tape it to coat hanger wire, bend to the necessary angle. They even have built-in LED lighting.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Thanks for the tip Pid, I’ll definitely check those things out. Imagine they’d end up paying for themselves many times over.


Sent from my iPhone using DO THE TON
 

doc_rot

Oh the usual... I bowl, I drive around...
DTT SUPPORTER
DTT BOTM WINNER
I dont bother running inline filters anymore myself. They don't really seems to strain the small stuff and the filter at the petcock does a good enough job. I would be surprised if any of that small stuff would block the jets. but its worth the time to inquire. Take a look at your gas cap and make sure its venting properly.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
How can I check if the gas cap is venting properly Doc?

I noticed that the paint and clearcoat around the mouth of the tank is bubbling a bit. Is that a sign of something?
 

Maritime

Over 10,000 Posts
gas cap check is usually pop it open and see if the bike runs better but you can't do that method right now. You can put gas in tank, put fuel line on petcock into a container, open petcock and watch flow, if is starts to slow down after a few seconds and or starts to pull air back up the line then open the cap and it flows better again your vent is buggered. Poor venting will starve the carbs and make the bike crap out when you open the throttle.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
I did run that check while the tank was still on the bike and hooked up to the carbs. Removed the cap while the bike was running, but it didn't make any difference at all. Still ran like crap. I'll try the other method you mentioned to be sure.

I do find it odd that the rust had made it past two filters (one on the petcock and the other inline), and that neither filter showed any signs of collecting any garbage, but hey. Charlie made a good suggestion that maybe the problem had arisen downstream of the inline filter, but I know I thoroughly cleaned the lines and the diaphragm assembly on the carb rack itself.
 

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