1988 DR750 Big rebuild
#11
Interesting read keep us informed
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#12
The carbs have now been cleaned to within an inch of their lives. Replaced the o rings at the bottom of the plastic guides. have blown air through every hole. Did this with the carbs underwater so I could made sure the air was coming out somewhere else.
I got some clear plastic tube to try and wet check the float level. I can not get the fuel level to sit at the mating face of the carb base. I adjusted and adjusted the float, even trying to make it massively wrong but nothing really seemed to make much difference. the fuel level was always above the gasket level. I have ordered some repair kits to replace the float needle and seat although the ones fitted seem ok and i did swap out one for a spare i had from my bmw650. I have also ordered a set of carb cleaning needles to just try and make sure the pilot's are clear, although the carbs were spotless after a good hour in the ultrasonic bath.
Im starting to think the issue is not with the carbs?. I rechecked the valve clearance, as I had done it when I put the head on, If anything the gaps were very slightly to big. I adjusted and still no improvement.
Ive read through all the 750 and 800 posts and im stumped at the minute. Will see if the carb kits help. Will also check the compression just in case.

carry on :O)
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#13
Have you got a compression tester?
It sounds like you have done a thorough enough job on the carbs (if the prob isn`t related to the fuel level....) and the unwillingness to keep running at idle speeds may have a more oninous source.
A quick check of the health of the cylinder/valves/top end would quickly eliminate any problems there, if it`s getting a bit tired `up top` or have a damaged valve seat for instance it might not be able to run at low revs.
Worth a check for such a simple test?
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#14
(20-11-2020, 12:01 AM)Hann Wrote: Have you got a compression tester?
It sounds like you have done a thorough enough job on the carbs (if the prob isn`t related to the fuel level....) and the unwillingness to keep running at idle speeds may have a more oninous source.
A quick check of the health of the cylinder/valves/top end would quickly eliminate any problems there, if it`s getting a bit tired `up top` or have a damaged valve seat for instance it might not be able to run at low revs.
Worth a check for such a simple test?
Thanks, Ive ordered a basic compression tester from amazon so will see what that shows. The engine has only done 18000 miles and when I striped it to replace the crank case the condition seemed to reflect the miles. I reground the valves as i precaution but again was very little wear there.

Unless I made a hash of the piston rings, but then it seems to run well at over 2000 rpm. I think I will go back over the timing and make sure thats correct also
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#15
This morning in at attempt to eliminate the carbs from the equation I borrowed the carbs from my BMWF650 (was trying to avoid that as the carbs are a git to get off and even harder to get back on without stripping half the bike) . It uses exactly the same carb, although obviously different jets. The BMW Runs and I thought at the very least the DR should run, albeit badly, with the known good carbs on.
No joy. Still just seems to cut off under 2000rpm. I stuck my gunson autotune plug back in and sure enough it indicated was a little lean when running over the 2000rpm (which I expected as jetted for a 650) but at soon as the revs drop it looks like the spark just disappears.

Back to the drawing board...
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#16
had the covers all off and checked the timing again and all spot on
tested the cdi box and coils as per the official suzuki manual and again all seems ok there.

that's it for now until my carb kits and compression tester turn up
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#17
I`d somehow missed the fact that you`ve rebuilt the whole motor so if there was anything seriously amiss with the top end i`m pretty sure you would of spotted that at rebuild time..... Doh.

Do you think the spark is cutting out at these low engine speeds?
One of those plug caps with a light built in might be of use?
I was going to suggest a few quick electrical tests next but it seems you`ve already done them?
Coil primary is very low usually - about 1 or 2 Ohm.
Coil secondary 10 - 17KOhm. Thats quite a wide tolerance. I wonder whether that includes any plug cap resistor? I`d remove the plug cap to the check secondaries.
Pickup/pulser coil resistance 175 - 265 Ohms.
CDI power source coil - 230 - 355.

I recently had an NX650 Dominator which was a bitch to start but once running was fine - cause was a failing/tired CDI unit, luckily only 20 quid pattern part.
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#18
(20-11-2020, 07:04 PM)Hann Wrote: I`d somehow missed the fact that you`ve rebuilt the whole motor so if there was anything seriously amiss with the top end i`m pretty sure you would of spotted that at rebuild time..... Doh.

Do you think the spark is cutting out at these low engine speeds?
One of those plug caps with a light built in might be of use?
I was going to suggest a few quick electrical tests next but it seems you`ve already done them?
Coil primary is very low usually - about 1 or 2 Ohm.
Coil secondary 10 - 17KOhm. Thats quite a wide tolerance. I wonder whether that includes any plug cap resistor? I`d remove the plug cap to the check secondaries.
Pickup/pulser coil resistance 175 - 265 Ohms.
CDI power source coil - 230 - 355.

I recently had an NX650 Dominator which was a bitch to start but once running was fine - cause was a failing/tired CDI unit, luckily only 20 quid pattern part.
That's the problem I guess with a near 40 year old bike. Cant easily locate spares or they not really cheap enough to just throw at it with out at least having some doubt over the function of what your replacing. Also had a college lecturer who was a stickler for diagnostics and didnt believe in replacment without first proving the part was faulty or out of tollerance.
The factory manual I have located matches what you mention for the Ohm figures, it also states that if your not using the exact suzuki tester you may get varying figures.
When I tested the coils both primary were around 0.8 Ohm (manual I have says 0-1 Ohm) the secondary'sys were around 9 Ohm (against 10-17 Ohm to plug cap it says) so im a bit low.
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#19
Photo 
The compression tester arrived this morning so straight to work

The manual says warm the engine but I cant as the carbs are on the bench SO im going with what I know....

Cold test was 185psi , I then put some oil down the bore and did a wet test....220psi

I decided to do the wet test as I suspect the bores have been washed clean with trying to start it repeatedly. So even the dry test was above spec (Min 142psi)

https://photos.app.goo.gl/Y3TzqXDw4kVHspHh8
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#20
And spend the last two hours swearing at the carbs...

I got new o rings and float needle and seats. Got one side done ok I think, but the the other side...the side with the choke .... Ive been through 3 floats, including the what looks like new one that was in the carbs and can not get the level correct...or should I say that whatever I do , however I set the float, it overflows.

I have even had the carb set up with the floatbowl off it and fuel connected (on the bench) and manually moved the float by hand and it stops fuel flowing. as soon as I put the bowl back on....it overflows.
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