rickg
Junior Member
Posts: 31
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Post by rickg on May 18, 2008 22:43:43 GMT -5
Just picked up a lightly wrecked 79 sr. I am using my spare parts to put it back on the road. My question is how to best use the stock petcock and an after market flat slide that does not have a vacuum port to operate the petcock. I can run it on prime as the previous owner did but would like the reserve to function, is there a non vacuum petcock the fits the stock tank? Or what is the better way to do it? Rick
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Post by solo2racr on May 18, 2008 23:52:07 GMT -5
What I did with mine is to do away with the diaphragm, spring, & rear cover and fabricate a new rear cover from sheet aluminum. Upon doing that, figure out which passage is what (ON, RES, PRI). When you get sorted, use a bit of JB Weld and block off the PRI passage. That will be your OFF position. The other two will be the same as before.
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Post by colinjay on May 19, 2008 1:27:48 GMT -5
Back in the early 80's, when I first fitted the EI flatslide carbie to my SR, I drilled a hole into the side of the carbie (engine side of the slide) and fitted a small brass barb to take the same size rubber tube as the std fuel tap vacuum line. This allowed the std fuel tap to be used and has never given any problems.
CJ
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Post by stevec5000 on May 19, 2008 8:22:01 GMT -5
You can replace the stock petcock with a Pingel that has Off, On and Reserve commonly used on Harleys. I have used them on my SR, XS1100 and 750 Seca. The one for a YZ80 should fit. You can either get one that includes the mounting bracket or make one yourself. The stock ones didn't allow enough fuel to flow and I kept running out while driving at high speed on the freeway. The Pingels have a hole nearly 1/4" in diameter straight down through them when open so there's nothing to impede the flow of fuel. I found that Pingel model 4111-AH4 for the Yamaha YZ-80 was a perfect fit on my XS1100 Midnight Special. The 4111-AH4 model has On-Off-Reserve, an aluminum hex shaped body with 1/4"NPT threads and single outlet and includes the mounting bracket with holes spaced 34mm apart. The larger and more common models with 3/8" threads like those used on Harleys could be installed also
The slotted hole in the tank needs to be wider in the middle to allow the filter to go up through the hole but otherwise they bolt right on. I used a small sanding bit in my Dremel tool to cut out some material from the center of the hole. Take care with the 4111 petcock since the body and threads are aluminum and the threads are very delicate. Do not screw it into the aluminum mounting bracket without putting something on the threads to keep it from sticking (or some teflon tape or form-a-gasket sealant when you get ready to install it) because the aluminum will gall and tear out the threads when you try to unscrew it. One of the Pingels came with a bracket that was a perfect fit on the 1100's fuel tank but the other one didn't so I made one from a piece of aluminum bar stock. It's fairly simple to cut it out the same size and drill the holes for mounting screws and drill and tap the hole for the Pingel. After it was all machined to fit I polished it up some on a belt sander to take off the rough edges. I got my Pingels on ebay and they aren't stocked by most dealers but can be ordered directly from Pingel for $79.80 which includes both the petcock and mounting bracket.
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Post by spindlehead on May 19, 2008 10:07:21 GMT -5
I did the same thing as Steve except that I used a cheap0 universal on-off-res petcock instead of the high flow Pingel. I had to file out some material from the center of the tank slot too. Flow has been fine so far. I got mine from partsnmore.com for $35 for the petcock and adapter. www.partsnmore.com/cat_index.php?model=ttxtsr500&category=carb |
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Post by chew652 on May 19, 2008 17:19:27 GMT -5
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Post by colinjay on May 19, 2008 22:39:19 GMT -5
Just a few thoughts on fuel flow, as for many years I ran the hot engine now in my race SR on the street using the STD fuel tap and never had any problems with fuel flow.
The maximum fuel flow thru a carbie is controlled by the main jet size (if you have the correct size float needle and seat). With a normal (large hex) mikuni jet the size of the jet is the fuel flow in cc(ml)/min, i.e. a #270 main jet flows 270cc(ml)/min. Therefore (in theory), with a #270 MJ, if you have the throttle held fully open the engine is consuming 270cc(ml) of fuel ever minute and that is all that the fuel tap needs to flow to stop the engine starving for fuel. Now I can’t remember exactly, but years ago I did flow test the STD fuel tap on the SR and from memory it flowed over 1 L/min.
I have calculated the fuel flow requirements for running the SR racer at Lake Gairdner using a 38mm Mikuni with a #270 main jet fitted (setup on a dyno for sustained full throttle operation, i.e. rich) with the bike geared to give 130mph (210kph) at 8000 rpm. Now the short course used by vehicle running under 175mph is 4 mile long, being a 2 mile run up, 1 mile timed section and a 1 mile slowdown. So in reality the time spent running flat out for the timed mile would be about 27.6 second (at an average of 130mph) which would give a fuel usage of about 135cc(ml) for the timed mile. Allowing for a couple of minutes to accelerate up to speed with the throttle full open except for gear changes and that it would be foolish to just slam the throttle closed at the end of the timed mile, it has been calculated that the overall time on the course would be about 4 minute, which translates to just over 1 litre of fuel require to run the course.
If you translated 4 minutes at 130mph (210kph) to distance traveled It equates to 8.6 miles (14km) on the 1080ml of fuel, but I don’t think there is anywhere that you could do that kind of run.
Getting back to fuel flow for a normal bike, three common reasons for low fuel flow through a fuel tap are;
1. a blockage / build up of dirt and rust around the fuel filter that sticks into the tank,
2. leak vacuum line / faulty diaphragm not letting the tap open fully,
3. a blocked air vent in the fuel cap not letting air in quick enough to replace the fuel flowing out via the fuel tap.
It is always worth checking these 3 before just blaming the tap for not being able to flow enough fuel. And in the case of engines that do require a lot of fuel, you should also look at fitting a full flow air vent line to the fuel tank and a bigger float needle/jet into the carbie to make sure that you can get the correct volume of fuel to the main jet.
CJ
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