Topic: CB750 F1 Stalls in first gear

[Seeparkfly]

I did quite a bit of searching but mostly found folks with stuck clutch issues. I don't think I have that problem since I can shift through all the gears just fine, and it doesn't pull while in neutral. Finding neutral is easy by the way.

I cleaned carbs, replaced spark plugs and caps, adjusted the tappets and cam chain, and timing (static). Double checked all of it and then installed HM ignitions, and after adjusting the clutch cable according to the manual. While on the center stand the bike shifts through all the gears, and when the clutch is disengaged the wheel doesn't move. I decided to take it on its maiden voyage around the block and found problems:

- The bike keeps stalling right away in 1st gear when engaging the clutch. I rev it and finally get it going after some stalling to find that it rides and shifts fine (to my knowledge, I'm a newbie)

- The new battery died under 2 miles and made the bike stall over and over again. Had to kick start it several times to get home. I parked it and kick started it and it idled. Some surging between 1200 and 2500.

When the rain stops I will clean the contacts for the rectifier, regulator and fuse block, along with the battery ground to the frame. I've already cleaned the contacts for the coils and both handle bar switches.

If there is something I am missing please let me know. I do have new condensers. The old ones seem worn but wouldn't the HM ignitions override them?

[HondaMan]

First: did you check the timing with a timing light? The points gap should be in the range of 0.012" to 0.016" and the "F" marks line up at idle speeds. The 750F bikes sometimes advance past their full advance marks at speed, but that won't affect idle issues.

About the Hondaman Ignition portion: if the condensors are bad, the bike tends to idle quite fast, and won't rev up past about 4000 RPM. You can simply disconnect them as a test, to see if they make any difference. In the end, run with them connected for best results on the street.

But, this doesn't sound like condensors. It could be several things.

First, vacuum leaks in the hoses where the carbs are mounted can make the low-speed power very weak. These are often real hard from age now. Make sure the existing clamps are at least tight (all 8 of them), but I wold recommend getting some stronger, wider hose clamps (1/2" wide radiator clamps) on at least the head side of those hoses, and clamp it tight.

Second, the setting of the idle air screws (idle fuel screws, if they are PD carbs) is critical to idle power. If the carbs are type 7A (with no accelerator pump) or earlier (657B) types, the air screw should be set at 1 turn out. If they are PD41 carbs, start at 1-3/4 turns, can be as much as 2-1/2 turns. The tiny O-rings up inside those idle screws on the PD carbs are often cracked from the ethanol fuels we are all suffering, and need to be replaced or it will never idle with any torque, period.

Finally: warped clutch plates can make the engine drag the transmission when in gear with the clutch pulled in, which makes idle real testy. The idle would work OK if in neutral in this case, but die (or tend to die) when dropped into gear. Also, if the bike has been sitting a long time, the plates may be stuck together for quite a while until the engine gets run up to temperature a few times to spread oil through the plates again. When it sits for years, it squeezes all the oil out of the cork plates, making for poor disengagement and lots of clutch drag in gear (with the clutch pulled in).

[Seeparkfly]

First: did you check the timing with a timing light? The points gap should be in the range of 0.012" to 0.016" and the "F" marks line up at idle speeds. The 750F bikes sometimes advance past their full advance marks at speed, but that won't affect idle issues.

About the Hondaman Ignition portion: if the condensors are bad, the bike tends to idle quite fast, and won't rev up past about 4000 RPM. You can simply disconnect them as a test, to see if they make any difference. In the end, run with them connected for best results on the street.

But, this doesn't sound like condensors. It could be several things.

First, vacuum leaks in the hoses where the carbs are mounted can make the low-speed power very weak. These are often real hard from age now. Make sure the existing clamps are at least tight (all 8 of them), but I wold recommend getting some stronger, wider hose clamps (1/2" wide radiator clamps) on at least the head side of those hoses, and clamp it tight.

Second, the setting of the idle air screws (idle fuel screws, if they are PD carbs) is critical to idle power. If the carbs are type 7A (with no accelerator pump) or earlier (657B) types, the air screw should be set at 1 turn out. If they are PD41 carbs, start at 1-3/4 turns, can be as much as 2-1/2 turns. The tiny O-rings up inside those idle screws on the PD carbs are often cracked from the ethanol fuels we are all suffering, and need to be replaced or it will never idle with any torque, period.

Finally: warped clutch plates can make the engine drag the transmission when in gear with the clutch pulled in, which makes idle real testy. The idle would work OK if in neutral in this case, but die (or tend to die) when dropped into gear. Also, if the bike has been sitting a long time, the plates may be stuck together for quite a while until the engine gets run up to temperature a few times to spread oil through the plates again. When it sits for years, it squeezes all the oil out of the cork plates, making for poor disengagement and lots of clutch drag in gear (with the clutch pulled in).

Wow, thank you Mark. So not with a timing light b/c I don't have one but did statically time it. It took multiple adjustments but got it at the "F" mark. Points were gapped .013"

Bike revs up passed 4,000 rpm just fine but I'll replace those condensers just to be safe.

As for the Carb boots, I did the wintergreen treatment successfully and tightened the clamps good. Today I sprayed some carb cleaner around the boots. This didn't change the idle at all. No leaks around the exhaust either. Will check again tomorrow.

I don't know what kind of carbs I have,  I believe they're original to the F1. Have pics of them here http://forums.sohc4.net/index.php?topic=97084.0 The idle air screws were set 1 full turn out. Are the o-rings deep under the springs?

At this point I think the stalling issue may be the clutch plates. I don't have drag problems with the clutch pulled in though. Today I did noticed 1st gear grinding. Clutch pulled in sometimes grinding sometimes not. I can shift through all the gears fine but sometimes it feels like the clutch isn't disengaging with 1st and 2nd, but again sometimes it's fine. By the way, it stalls in 1st when off the center stand, but when on the stand with some rear brake engaged it won't stall. Guess it needs more torque to push me and the bike forward.

It's almost there and I'm anxious to get it running properly. Tomorrow I'll pull the clutch and examine. Is it necessary to drain the oil, or can I just place a pan underneath and expect that only some of the oil will come out? I'll also take the idle air screws and springs out to search for o rings. Any guidance will be much appreciated.

[HondaMan]

First: did you check the timing with a timing light? The points gap should be in the range of 0.012" to 0.016" and the "F" marks line up at idle speeds. The 750F bikes sometimes advance past their full advance marks at speed, but that won't affect idle issues.

About the Hondaman Ignition portion: if the condensors are bad, the bike tends to idle quite fast, and won't rev up past about 4000 RPM. You can simply disconnect them as a test, to see if they make any difference. In the end, run with them connected for best results on the street.

But, this doesn't sound like condensors. It could be several things.

First, vacuum leaks in the hoses where the carbs are mounted can make the low-speed power very weak. These are often real hard from age now. Make sure the existing clamps are at least tight (all 8 of them), but I wold recommend getting some stronger, wider hose clamps (1/2" wide radiator clamps) on at least the head side of those hoses, and clamp it tight.

Second, the setting of the idle air screws (idle fuel screws, if they are PD carbs) is critical to idle power. If the carbs are type 7A (with no accelerator pump) or earlier (657B) types, the air screw should be set at 1 turn out. If they are PD41 carbs, start at 1-3/4 turns, can be as much as 2-1/2 turns. The tiny O-rings up inside those idle screws on the PD carbs are often cracked from the ethanol fuels we are all suffering, and need to be replaced or it will never idle with any torque, period.

Finally: warped clutch plates can make the engine drag the transmission when in gear with the clutch pulled in, which makes idle real testy. The idle would work OK if in neutral in this case, but die (or tend to die) when dropped into gear. Also, if the bike has been sitting a long time, the plates may be stuck together for quite a while until the engine gets run up to temperature a few times to spread oil through the plates again. When it sits for years, it squeezes all the oil out of the cork plates, making for poor disengagement and lots of clutch drag in gear (with the clutch pulled in).

Wow, thank you Mark. So not with a timing light b/c I don't have one but did statically time it. It took multiple adjustments but got it at the "F" mark. Points were gapped .013"

Bike revs up passed 4,000 rpm just fine but I'll replace those condensers just to be safe.

As for the Carb boots, I did the wintergreen treatment successfully and tightened the clamps good. Today I sprayed some carb cleaner around the boots. This didn't change the idle at all. No leaks around the exhaust either. Will check again tomorrow.

I don't know what kind of carbs I have,  I believe they're original to the F1. Have pics of them here http://forums.sohc4.net/index.php?topic=97084.0 The idle air screws were set 1 full turn out. Are the o-rings deep under the springs?

At this point I think the stalling issue may be the clutch plates. I don't have drag problems with the clutch pulled in though. Today I did noticed 1st gear grinding. Clutch pulled in sometimes grinding sometimes not. I can shift through all the gears fine but sometimes it feels like the clutch isn't disengaging with 1st and 2nd, but again sometimes it's fine. By the way, it stalls in 1st when off the center stand, but when on the stand with some rear brake engaged it won't stall. Guess it needs more torque to push me and the bike forward.

It's almost there and I'm anxious to get it running properly. Tomorrow I'll pull the clutch and examine. Is it necessary to drain the oil, or can I just place a pan underneath and expect that only some of the oil will come out? I'll also take the idle air screws and springs out to search for o rings. Any guidance will be much appreciated.

It does sound like warped clutch plate(s). On bikes that sat a long time, it's pretty common. You can test them with feeler gages and a piece pf plate glass for a "flat block" by laying the plates, one at a time, on the glass and attempting to slide a feeler gage in under the highest point. If more than .004" warped, they will drag: at .006" they drag quite a bit. Honda calls for replacement at 0.013", but by then you can barely shift the gearbox, in my experience.

It looks like you have the 7A or 657B carbs. I would advise losing the fuel filter, though. There should be a screen in the fuel petcock on the tank already. The air screws should be set at 1 turn out. Make sure that your sparkplugs are not sooty black: if so, get new ones. Old gas can foul the plugs in a matter of minutes these days. If they are blackened, get some D7EA or X22ES-U plugs for a while (hotter) to help keep them cleaner until you get it all sorted out. Then you can switch back to the D8EA or (best) X24ES-U from Nippon Denso.

[Seeparkfly]

Just returned from an interesting party for a launch of graphic novel app for the iPad. I ended up going b/c I accidentally locked myself out after deciding to examine the bike some. Anyhow, I believe I may have found what the problem is.

I fired it up, checked the headers and guess what, only 3 and 4 were hot. Huh, I cleaned those contacts with a wire brush and used dielectric grease. I unplugged the HM ignition box and found 1,3 and 4 firing but not 2. Weird. I cleaned all the contacts, even crimped down on a few so they'd snap in. Well, the plan is to check the plugs, put a different on in 2 and go from there. I hope the clutch plates are just stuck and not warped.

If anybody has experienced this and knows what's going on do share.

[Seeparkfly]

Fixed it and took it for a spin today. 

Stalling issue was due to cylinder 2 not firing. Found out by touching the number 3 header with my glove and burned part of it, but it wasn't till later I checked the others. It was there right under my nose the whole time. The problem wasn't the condensers, electrical connections, or clutch, it was carb 2 not getting any fuel. I took it apart and found gunk in the little screen that attaches to the seat for the float needle. Looking back I recall cleaning the tank with acetone and feeling like I cleaned off the liner that was put in by the PO. That glue like substance got into the carbs even after rinsing the tank pretty well. Cylinder 1 started working after unplugging HM ignitions, and continued to work after reconnection. Finally. Now enjoy the ride for a while till funds appear and then mod the seat, tank and all sorts of other things.