question for Cotten or anyone carb guys

[poorbiker]

Some 4 months ago I decided for no particular reason to remove my m74 and transfer everything over to a pristine m74 body, throttle disc area was a concern on old carb body, end flanges perfect.
Bike starts and runs strong, as good as my 62 or 69..no popping, no issues except I was on one of my annual trips to the mountains when on a grade I had been on many times with my knuckle it
started running out of power until it stopped, never dies, after a bit back on the road, then happens again on grade. tried enriching it, no go, checked for vapor lock on tank, not a thing. fuel filter
good, plenty of fuel. when at altitude and not on a grade does fine, starts fine, not overheating.
only difference since last on that route was carb swap. went back through carb can find nothing.....plenty of power. running magneto, pushrods adjustment good, what the hell have I
missed....short of re-installing old carb body, any ideas.....I know, should have left it alone but that's the mechanical tweaker in all of us, lol....

[T. Cotten]

Poorbiker!

Altitude may be the key, as the funky little HS needle supposedly was to tune for such things, by leaning out the mixture. The air is less dense, and requires less fuel.

(None the less, my philosophy is that all the little things can add up,... so I leave no stones unturned. Arbitrarily swapping parts is a recipe for a tail chase.)

....Cotten
PS: You really meant both were M74Bs, right? The M74 had a different HS needle.

[poorbiker]

No, the first one was just the 74 replaced it with the 74b as per a pervious conversation between us in never could find the proper needle for the 74 so I just ran the 74b needle. Swapping over to the b I supposed would clear up the needle issue and body on the b was like new...I was running hi speed needle about 1/4 turn out.

Altitude may be the key, as the funky little HS needle supposedly was to tune for such things, by leaning out the mixture. The air is less dense, and requires less fuel.

(None the less, my philosophy is that all the little things can add up,... so I leave no stones unturned. Arbitrarily swapping parts is a recipe for a tail chase.)

....Cotten
PS: You really meant both were M74Bs, right? The M74 had a different HS needle.[/QUOTE]

[T. Cotten]

Poorbiker!

Next time, turn the HS inward, leaning it instead of enrichening. The air is thin at high altitudes.

....Cotten

[poorbiker]

Ya I run it almost off, shutting it off was my first reaction but it didn't change a thing, so I tried enrichening it, nothing...
Thnx.

Next time, turn the HS inward, leaning it instead of enrichening. The air is thin at high altitudes.

....Cotten[/QUOTE]

[rousseau]

poorbiker

What I understand from your post is the bike runs fine unless you are going up hill (grade) in the mountains (altitude)or otherwise. If this is correct then I would suspect the float level.

[T. Cotten]

Here's what the Manual says, Folks,

(attached)

Down a grade isn't likely to bog a bike down, is it?
There's only one float level, ¼", unless something's wrong with the float.

....Cotten

[poorbiker]

As I said I never actually turned it all the way off as it was at a 1/4 turn out to start with. Didn't think turning it off would make a difference. Felt like fuel starvation but with the popping and jerking associated with running out of fuel..just steady loss of power to a stop, then normal..thought float level but set correctly...strange that bike runs so good except at altitude on a grade....have gone back through carb, everything good, venturi tight no gaps....no popping in carb or exhaust..problem since I changed carb body...

[poorbiker]

Update, I believe I have found the issue. I thought it was over fueling but could not find it to be the case. Removed carb and went through it thoroughly. No issues. On further inspection I found a metal (brass) drill twisting in bottom of inlet, on bottom of it was some rubber gunk. It was occasionally and inexplicably hang up in the float needle, but only while pulling a grade, way too much fuel was getting through carb combined with altitude caused a lack of power and an odd muffled exhaust note, though I haven't been back in altitude to prove this out. Don't have any idea how material got by filter, maybe picked up off of work bench....I guess drilling would rise and fall at different times hanging up the needle...