Sf1 36mm PHF carb tuning

Canuck750

Canuck750

Full member
Location
Edmonton, Alberta, Canada
I have a 1973 SF1 with a pair of  new round slide PHF 36mm replacement Dellorto's. Carbs are jetted to stock specification. Bike starts right up from cold with a little choke, but Its not running great and the left cylinder is cutting out. There is a spit of fuel intermittently popping out of the left side of the left carb overflow hole. On the road in second or third gear if I give it a full twist of throttle it just bogs and lacks power.

Some background on the bikes condition:

The Ignition has been replaced with a Witt unit and the coils replaced with 5 Ohm Dyna coils, new copper core high tension leads. With the Witt on test position '0' I get a strong spark out of both plugs. The engine has been overhauled (bottom end refresh by Wolfgang Haerter)new primary chain, clutch etc..., valve job done to the head, new rings, 150 psi compression on both cylinders. New fuel lines and petcocks, cleaned and sealed gas tank. Throttle  has been cleaned and lubed, throttle cables are new and lubricated and are not binding, I have a couple mm of slack in the throttle cables where they enter the top of the carbs. Slides snap closed easily.

My knowledge of tuning is very limited, can anyone explain why I am getting fuel occasionally spitting out of the side of the left carb?

Thanks

Jim
 
I imagine you have already set the ignition timing, valve clearance and float height. I would then disconnect the pump (debatable but helped my SF3). Then pull one plug, screw up the tickover screw on the other cylinder so that it will idle on that cylinder and adjust the air screw in and out until you get the best running, repeat on the other cylinder. Finish off by balancing with a manometer.
 
Are both exhausts getting equally hot? Sounds like it?s dropping on to one cylinder under load and the popping and spitting is back pressure causing carb to flood . Check basics like air leaks around manifold  by spraying WD40 on joints and see if it comes on song or starts sucking at joint and check that the fuel taps are properly flowing and not bunged up with tank sealant( had that ) . If you run bike with neon plug caps you can see if it stops sparking under load. That?s what I would start with.Jason
 
Does it overflow fuel just sitting there not running? Take off the left float bowl, and manually raise and lower the floats when you open the fuel tap, you will be able to see if the float needle is closing properly. Check the washer under the seat as well, just because they are new......
It is easiest to check float levels with the carbs off, and that is pretty easy too.
 
Thanks Fellas, I will check the float height and fuel valve. I had set the valves and timing but will check both again. I think the left is cutting out under load, the mufflers are both hot while the bike idles on the center stand but there is popping from the left side, cutting in and out. I took it for another 15 minute ride and pulled the plugs, the right is rich - sooty black and the left looks likes its lean or hardly burning at all.

I will go through it all again tomorrow.

Thanks again for the help,
 
I'd start with float height - you may have fitted all the right jets, but the float heights may have been neglected. New carbs ere set up for what - slides? pilot jets? main jets? needles? etc etc?

What # slides did they come with? Either a 60/- or a 50/ should work with an SF1. The second number after the / is the accelerator pump ramp position - you can ignore this, especially if you take the advice of many on here and remove the pin that secures the pump lever and spring (thereby removing the pumps from the sys altogether - you earn a lighter throttle action and lose nothing).

It should have 60 pilot jets IIRC - someone please correct me if I'm wrong with that number. Oz SF2s came with 45s and they were a nightmare for popping back through the carb when lifting off idle; fitting 60s worked miracles.

When setting the mixture screw, it's a good idea to screw in until it drops sped then out to find the highest idle speed. Then screw out (richen) by 1/8 to 1/4 turn to assist with pickup off idle. idle speed will drop slightly but it won't matter as this can be easily compensated with the throttle speed screw.

If you're really lost in all this, try and find someone au fait with Dells - problems are usually easily solved if you're familiar wth them, not so if it's all clutching at straws for you.
 
I went back out to the shop and pulled the carbs off, after removing the float bowls I was shocked to see a pile pf grey crud in each bowl. I had just got the gas tank and side panels back from my painter and he had also sealed the tank with Por-15 tank sealer. The tank was clean inside and rust free but my painter swears by a thin coat of Por-15.

Obviously some of the Por-15 had not set and the fuel turned it to a very fine particle that got past the petcock filters and the carb filter. I drained about a 1/2 cup of the crap out of the 8 liters of gas I had in the tank. This liner material was starting to restrict fuel getting into the carb and had I ran the bike much longer the petcocks would probably have plugged right up.

The liner particles are heavier than the fuel so it appears the crap did not get drawn up into the carb but collected in the bowls and the bowl cap nut.

Stripped the carbs and petcocks down and put everything in the ultrasonic tank for an hour then rinsed and blew everything out.

Now the gas tank has to go back to the painter to have the liner stripped out, DAMN!!!!

I have another tank I can fit while I wait for the freshly painted tank to get cleaned.

I did check the float height and they were a bit high at about 20mm, I reset them to 18mm.

The idle jets are #60, Wolfgang Haerter had set the carbs up with all the internals so I am pretty confident he has fit the appropriate components.

I don't follow the instruction to disable the accelerator pumps,  to disable the pumps do I take out the accelerator pump jet inner component? by this I mean the brass nipple that goes into the carb body 1st but keep the outer half that seals the opening in the body? Do I leave the diaphragm and spring in?

I checked the valve clearances, all are bang on.

Tomorrow I will fit the spare tank, reinstall the cleaned carbs and check timing, set the mixture and idle.
 
No, you remove the plastic arm attached to the top lid of the carb, that activates the pump. You remove the pin that holds that arm to the carb lid. Take care as there is a tiny spring between that arm and the carb in there that is easy to lose. It really reduces the strength of the throttle pull. I leave them working or did when I had Dels, ask Ron. They wont wheely without the pumps.
 
That is a bastard about the tank, hope he can get it sorted. My practice with stuff like that is that if it isn't rusted or whatever, there is absolutely no need to line it.
SF2 and 3 came to Australia with #40 and they were too lean, needing 2 1/2 turns to idle. I use #45 and they are fine. Numerous bike I have helped with lately have come with #60 pilots and are too rich, I have fitted #45 to these and they are great, 50 would be as big as I would go here, but maybe different countries have different fuels, but do they suddenly need much bigger mains and richer needles for that too?
 
Tippie said:
That is a bastard about the tank, hope he can get it sorted. My practice with stuff like that is that if it isn't rusted or whatever, there is absolutely no need to line it.
SF2 and 3 came to Australia with #40 and they were too lean, needing 2 1/2 turns to idle. I use #45 and they are fine. Numerous bike I have helped with lately have come with #60 pilots and are too rich, I have fitted #45 to these and they are great, 50 would be as big as I would go here, but maybe different countries have different fuels, but do they suddenly need much bigger mains and richer needles for that too?
Click to expand...

Maybe SF1s require the bigger pilot - they do run a different cam to the 2s and 3s.

Ditto re the bloody tank liner!! I'd rather spend days getting rid of rust before I'd go anywhere near tank liner - it can work, but if it doesn't I can easily see endless problemi with it.

Good news that you found the prob and hopefully it will soon be fully sorted.
 
Vince said:
No, you remove the plastic arm attached to the top lid of the carb, that activates the pump. You remove the pin that holds that arm to the carb lid. Take care as there is a tiny spring between that arm and the carb in there that is easy to lose. It really reduces the strength of the throttle pull. I leave them working or did when I had Dels, ask Ron. They wont wheely without the pumps.
Click to expand...

Thank you Vince!

What does removing the pump effect in terms of performance?
 
I have written about my Delordo experience on the 350 TE Husky a few times. That bike had a really jurky off idle drive I hoped to quire by disconnecting the pump-action and it did. It was way lighter and smother with it disconnected but the major downside was if you gave it a fist full it would bog and fall on its face, exactly what the pump was designed to avoid. Its designed to fill in for any sudden acceleration and allow the engine to respond HARD.That's a major issue on a dirtbike so it was reconnected. On Laverdas plenty say this is not needed and all it does is waste fuel and add friction to the throttle. Hence my joke about wheelying not happening with it disconnected. Not much jumping of logs done on Laverdas.
 
Piranha Brother 2 said:
Yeah, yeah, number is higher, fuel is lower ... don't confuse us, Paul!!  :-*
Click to expand...

You need to reason in terms of fuel height.
Lower fuel, risk of being weak but higher value of float height.

Seems important.

Paul
 
If you search the forum you will  find both pros and cons of the accelerator pumps. Either way you now know it's not your problem. Leaving them connected or not  should not affect the enjoyment of the bike. It will be a smooth ride either way once you get it sorted.
 
I spent the better part of the day driving to my painters town to deliver the gas tank and back home.

I did check all of the carb components, first I swapped the #60 idle jet for #54

Main Jet is 140
Needle is E17
Slide is 60/4
Atomizer is AB265

While I was in the carbs I did remove the pump pin/lever.

What is the recommended NGK spark plug for the SF1?

Is there a recommended ignition curve for the Witt Ignition?

This is what was in the float bowl



and the petcock filter



And what came out of the tank



 
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