Author Topic: Another AVL wakeup  (Read 11421 times)

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Adrian II

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Reply #15 on: March 20, 2019, 10:06:41 am
My understanding of the right thing...  ;D



Dell'Orto PHF36 pumper carb (the head needs surprisingly little porting work on the inlet side), the Malossi 02-0555 carb rubber bolts right on, just add stainless steel clip and motorcycle.

A.
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chuntera

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Reply #16 on: April 21, 2019, 06:33:30 pm
Hi All,
Another update. Finished going through the electrical; had to re-solder a few of the bulb ground wires, replace burnt out bulbs, etc. Sadly I broke the headlamp glass when moving equipment
around in the garage, so I replaced with a sealed beam headllight.

Got the bike back together, put about a gallon of fresh gas in the tank. Unsurprisingly the fuel tap leaked so I had to seal that up.

Finally got the bike started yesterday, there is more noise from the valves than I am comfortable with. I haven't checked the valve/pushrod clearances so that will added to the todo list.

It runs poorly, backfires when rolling off the throttle and bogs down when rolling on the throttle. I suspect a vacuum leak somewhere so will have to also check the carb boot, etc.
At least it idles. Once it warmed up I was able to start it without the choke.

Left it on the stand and ran through the gears, seems to shift OK and no problems finding netural.


chuntera

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Reply #17 on: April 26, 2019, 04:37:45 am
I checked the pushrod clearances; the intake was a little tight & exhaust was a little loose. I adjusted both tappets, the 3 nut locking mechanism is...interesting...difficult to dial in the clearance and lock down the tappet. There is less valve noise after adjustment (less being a relative term here).

I pulled the carb & intake boot to check for vaccum leaks and found no obvious problems. I discovered one of the screws for the intake boot was loose so maybe that was causing the air leak. Carb jetting is off, running rich at most throttle settings.

The front brake lacks stopping power. I replaced brake host with a SS line and bleed everything but still not happy with brake performance. I should check the caliper if the pads are moving properly on the pins.



Adrian II

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Reply #18 on: April 26, 2019, 12:59:23 pm
The 29mm CV carb would normally be deliberately jetted very lean to make the lean-burn set up with the restrictive exhaust header pipe function properly.

As your bike had been fitted with a freer-flowing muffler the previous owner could have jetted up the carb to suit. Does it still have the original header pipe? It would be double skinned and very heavy, with an obvious narrowing where it fits into the exhaust port on the cylinder head.

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


ace.cafe

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Reply #19 on: April 26, 2019, 01:09:55 pm
If you suspect an air leak, check the rubber diaphragm inside the top of the carburetor for any holes/rips/tears/pinholes/etc that may cause an air leak.
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chuntera

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Reply #20 on: April 28, 2019, 09:29:29 pm
The 29mm CV carb would normally be deliberately jetted very lean to make the lean-burn set up with the restrictive exhaust header pipe function properly.

As your bike had been fitted with a freer-flowing muffler the previous owner could have jetted up the carb to suit. Does it still have the original header pipe? It would be double skinned and very heavy, with an obvious narrowing where it fits into the exhaust port on the cylinder head.

A.

Thanks for the reply. I believe it is the OE exhaust header, appears to be double walled. There is a custom muffler that is shorter than stock (and louder).

The CV carb is defintely re-jetted. Stock jetting is 110 main and 15 pilot , mine has a 120 main and 17.5 pilot. The needle was raised (ie. clip was lowest position) and shimmed. These settings are too rich; my garage smelled of unburned petrol for hours :O

I set the needle back to original position (ie. clip in middle position) and will try 115 & 117.5 main jet sizes. My past experience jetting CV carbs was main jet +2 or +3 sizes, +4 sizes seems too much here.


Adrian II

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Reply #21 on: April 28, 2019, 10:08:04 pm
There has been stuff posted on UK forums about jetting up the CV carbs, but the guy who did it (portisheadric who posts here occasionally) had replaced the AVL down pipe with an unrestricted Hitchcocks' item, which the previous owner might not have appreciated. His notes are attached along with a piece about modifying the CV slide.

When the UK importers brought out their Electra-X go-faster kits they used a Dell'Orto PHF32 pumper carb. They opened out the front of the stock air box and fitted a bigger K&N air filter, but left the lean burn down pipe in place, which meant that the Dell'Orto still had to be jetted quite lean, only a 110 main jet ISTRC. I might have a Hitchcock's Electra-X Amal Mk1 kit going spare in a while if you want to play with that!

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


chuntera

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Reply #22 on: May 01, 2019, 02:26:27 pm
There has been stuff posted on UK forums about jetting up the CV carbs, but the guy who did it (portisheadric who posts here occasionally) had replaced the AVL down pipe with an unrestricted Hitchcocks' item, which the previous owner might not have appreciated. His notes are attached along with a piece about modifying the CV slide.
A.

Thanks for sharing the post about CV carb tuning which parallels my tuning experience so far. I have a 120 main jet, if I set the AF mixture screw 4-5 turns out, I have good throttle response from idle to 1/4 throttle. However using the "idle drop" method to set the AF mixture screw comes out around 2-3 turns out but engine will "bog"  or stall off-idle to 1/4 throttle.


tooseevee

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Reply #23 on: May 01, 2019, 09:57:39 pm
Thanks for sharing the post about CV carb tuning which parallels my tuning experience so far. I have a 120 main jet, if I set the AF mixture screw 4-5 turns out, I have good throttle response from idle to 1/4 throttle. However using the "idle drop" method to set the AF mixture screw comes out around 2-3 turns out but engine will "bog"  or stall off-idle to 1/4 throttle.


           Would you recap your present status on the carb for me? I've lost track.

           I know you have a short open bottle. What about intake?

           I think you're needing way too many turns out on that A/F mixture screw. Should run around 1 1/2 turns out plus or minus a quarter or an eighth (sound like a drug deal  :) )

            Zero to 1/4 throttle is all on the Pilot. Maybe you should try putting the Main back to 110, the Pilot back to 15, the needle to the middle notch.

            I think I remember I ended up (with open bottle and a K&N filter) leaving the Main at 110, a 17.5 Pilot, stock needle in the middle notch with one shim to make it a hair higher, mixture screw a hair more than 1 1/2 turns out. I didn't bother changing the Main as I never planned on getting anywhere near open throttle. It had  nowhere near any break-in miles on it.

             Whatever your particular recipe ends up being for your particular engine, it's a sure thing that your engine is getting way too much gas at that zero to 1/4 throttle opening. That's why it's bogging down. Remember to mark your throttle in increments.

             Oh Oh and you really must rule out vacuum leaks (but you know that)  :) :)
             
             PS: This tweaking of my BS-29 was way before the ACE headwork and switching to the TM 32. And the hot tube was yet to Dremeled out and disposd of unceremoniously with extreme prejudice.

             
RI USA '08 Black AVL Classic.9.8:1 ACEhead/manifold/canister. TM32/Open bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades.


chuntera

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Reply #24 on: May 05, 2019, 03:53:40 am
Would you recap your present status on the carb for me? I've lost track.

           I know you have a short open bottle. What about intake?

The bike has shorter  muffler than stock. The exhaust header pipe is double walled so I guess its the original one.
The air box has been removed and I have a Uni foam filter.

I think you're needing way too many turns out on that A/F mixture screw. Should run around 1 1/2 turns out plus or minus a quarter or an eighth (sound like a drug deal  :) )

            Zero to 1/4 throttle is all on the Pilot. Maybe you should try putting the Main back to 110, the Pilot back to 15, the needle to the middle notch.

I agree that going back to stock jetting is good move at this point. When I picked up the bike it had a 120 main, 17.5 pilot plus the needle had been raised & shimmed. So far I put the needle back in center notch without shim and went back to 15 pilot jet. Next will be reverting to the 110 main.

I think I remember I ended up (with open bottle and a K&N filter) leaving the Main at 110, a 17.5 Pilot, stock needle in the middle notch with one shim to make it a hair higher, mixture screw a hair more than 1 1/2 turns out. I didn't bother changing the Main as I never planned on getting anywhere near open throttle. It had  nowhere near any break-in miles on it.
I read some of your old posts which made me think stock jetting on the CV carb is probably good starting point.

Oh Oh and you really must rule out vacuum leaks (but you know that)  :) :)
Yup, had one of those, all better now :)


chuntera

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Reply #25 on: April 26, 2020, 05:06:21 am
Surprisingly I got this bike on the road today after ignoring it for the past 6 months.
Last fall I used a wideband O2 sensor to find reasonable carb jetting.
It appears the intake cam had been retarded by the PO, I reset to stock timing.
Apparently last year I didn't tighten a tappet locknut and the pushrod clearance had opened up. After another round of tappet adjustments, valve noise is noticeably lower.


ace.cafe

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Reply #26 on: April 26, 2020, 09:10:51 am
....
It appears the intake cam had been retarded by the PO, I reset to stock timing...

Yes, unfortunately after the cam retarding was popularized for the old CI Bullets, some people thought that they should do it to everything, which of course wasn't a good idea.
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Bullet Whisperer

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Reply #27 on: April 26, 2020, 01:54:08 pm
I have retarded the inlet timing on a few AVL engines when equipped with 'S' cams and a compression hike and it has worked out very well  ;)
 B.W.


ace.cafe

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Reply #28 on: April 26, 2020, 02:03:23 pm
I have retarded the inlet timing on a few AVL engines when equipped with 'S' cams and a compression hike and it has worked out very well  ;)
 B.W.
Hi BW,
Good to see you are doing well.
Maybe the virus lockdown will abate to allow some of this year's racing season. I always look forward to your success!
Home of the Fireball 535 !


Bullet Whisperer

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Reply #29 on: April 26, 2020, 08:14:44 pm
Hi BW,
Good to see you are doing well.
Maybe the virus lockdown will abate to allow some of this year's racing season. I always look forward to your success!
Thanks, Ace. I doubt we will be doing any racing this year, although the bikes are ready to go, excepting the cylinder head for the 350, which is undergoing repairs and upgrades.
 There is a lot of work underway here, but I have slowed it right down for now, as customers may not have so much money to spare at present and I am currently doing battle with some aches and pains which spring themselves on me from time to time, so this lockdown sort of suits me at present.
 Stay safe, all!
 B.W.