1988 DR750 Big rebuild

[Hann]

Those compression results are superb - especially for a cold engine..

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.

So something is impeding the floats movement when the float bowl is attached?

Hang in there - you`re nearly there!

[dougiehowser]

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.

I have even swapped the float and needle from the "good" side and visa versa....it still overflowed, and the side that I moved the "bad" side to was fine.

I can blow into the carbs and both sides will stop air/ the float and needle valve appear to function correctly until i add fuel....tired different floats, needles, carb bowls (as I have a set of BST33 that I took off my BMW650 to allow some parts on hand.

Im stumped. if the needle can function and stop air then why wont it stop fuel. I have done a wet level check with a clear plastic tube and you can see the fuel level rise over a second or two after filling and then overflows.

[dougiehowser]

So I was thinking the carbs must be damaged internally. I decided to try and eliminate the float needle. I took one of the old needle seats and blocked it completely , then fitted without the needle but installed tbe float. Bowl back on and tested ...not a drop of fuel in the bowl.
So it is the float / needle / seat that is somehow not closing when the carbs are assembled and fuel is added (as blowing air can be stopped)
When looking at the parts diagram there is a different part number for the floats. And one says LH the other nothing about handing. I looked at all the floats I have and can see no difference in any of them.
So £70 poorer and a pair of floats on the way from Japan in a few weeks

[dougiehowser]

So I was thinking the carbs must be damaged internally. I decided to try and eliminate the float needle. I took one of the old needle seats and blocked it completely , then fitted without the needle but installed tbe float. Bowl back on and tested ...not a drop of fuel in the bowl.
So it is the float / needle / seat that is somehow not closing when the carbs are assembled and fuel is added (as blowing air can be stopped)
When looking at the parts diagram there is a different part number for the floats. And one says LH the other nothing about handing. I looked at all the floats I have and can see no difference in any of them.
So £70 poorer and a pair of floats on the way from Japan in a few weeks

Im quite stubborn and after complete strip down, wash out , blow out and rebuild I finally managed to get the carb to stop overflowing. set the floats, put the carbs on the bike and went for a start. Which it did, with the same issue still. I have uploaded a video to my photos folder to show what it does.
I did a wet level test with the carbs on the bike and fuel level was showing stable at the split between the carb and bowl on both carbs.

So im almost certain its not the carbs, ive ruled out mechanical, so has to be electrical? After a lot of post reading I pulled the de comp unit. One terminal was quite badly corroded. By the manual it is #2, middle nearest the release clip, for the decomp lever. 
The bike starts so i assume its receiving the signal from the lever switch. I cleaned it up anyway and reconnected it. Still the same.
How much affect this "control unit" has on the continued running of the bike I cant figure out from the wiring diagram. It seems to collectively deal with all the fail safes and if correct it will allow power to the starter switch? but wiring diagram also has a connection to the CDI?

[dougiehowser]

So the big is going on the back burner for a couple of weeks until some parts arrive, I decided , after some dubious test figures to replace the CDI. I managed to get a full bottom end from France so now have a good set of starter gears. Some new floats coming and also managed to pick up another set of carbs just in case

Maybe can get her running for xmas then on with the frame and other stuff in the new year

[dougiehowser]

Hold the Phone!!!

I was just reading through this post in the DR800 section...

new parts fitted but now cuts out below 2000rpm

[b]denzily[/b]
Guest

 
#1
08-03-2014, 08:31 PM
Ok can anyone come up with any light on a problem I have with dr cutting out on tick over . if i turn the idle screw below 2000rpm it cuts out dead .I have today fitted a new mag and cdi unit and with great joy it now starts first time and revs up which it did not do before . But if I did manage to get it to start before fitting new parts it would tick over nice at about 1300rpm.
Any ideas would be very much welcomed



Further to that I took delivery of an engine bottom end this morning. While stripping the cover off to get at the lovely fresh starter gears I noticed the stator was not the same as what was on the bike. never though much off it until I read that thread.

Now I bought a new stator as the wires for the pickup where all frayed and the three yellow wires melted at the connection for both the stator and the reg/rec . I assumed what was on the bike was correct and ordered the same part going by picture.
BIG mistake. Basically there are two stators and they are not interchangeable due to CDI difference in years.

So what I think happened is the owner replaced the stator. I guess with a second hand unit judging by the state of the wires where they enter the case. IT was wrong so the bike did what it was doing for me and die under 2000rpm. Obviously during repeated attempts to start the bike the starter gears decided to leave the engine via the side of the case. game over. Probably never realised that the error was fitting the wrong stator.
So I run to the garage....quickly drain oil and just throw on the stator and cover of the engine I just got....boom...fire in the bloody hole. first turn no throttle, one click of choke and she fired right up... now I can get my teeth into this project

[ladder106]

Just read through this thread.

I’m impressed. Tenacious doesn’t seem quite strong enough.

Good work getting through this.

Is is possible for you to list the stator part numbers and the correct year(s) for each one so others don’t have the same problem in future?

[dougiehowser]

Just read through this thread.

I’m impressed.  Tenacious doesn’t seem quite strong enough.

Good work getting through this.

Is is possible for you to list the stator part numbers and the correct year(s) for each one so others don’t have the same problem in future?

Hi,
Looking back at it now its actually quite straight forwards, Just my foolish assumption that parts already fitted on the bike were correct. It appears there is only one correct stator for the 750. The other is for the 800 , although the 800 appears to use the same stator as the 750 in 1990 and then it changes.

I cant figure out how to have images in my post but the correct stator for the 750 is 3210144B00, for the 800 it is 3210231D00. I have pictures on my google photos link. Also you can actually see the difference on the parts diagram. The 750 has a large black post on the stator, The 800 has 2 slighly different colour posts. 
Hope that helps. There are some far more expert posts than this if searching the forum. Just takes a lot of trawling to find the jems of information ;O)

I bought the stator from electrexworld.co.uk as I have used them in the past for a Reg/Rec for my F650. Although when i reviewed the order they list the part when you search for DR750......but there is a note at the bottoms that says


[*]DR800 1991 on x 2 CDI source coil - Compare your stator with picture above.
[*]See repair part C102 for stators with only x 1 CDI source coil. DR750 & DR800 pre 1990 - see related products below.

I failed to pay attention to  this as I just looked at what was on the bike and it matched the picture.....lesson learned

[Dbldutch]

Amazing how a flash of inspiration can get things back on track again - Major kudos for perseverance!

[ladder106]

So in summary, the SR41 (Dr750) and SR42 (DR800 with original style bodywork) use the single CDI source coil stator.

The SR43 (DR800 with “updated” bodywork) uses the stator with 2 CDI source coils.

I’m still interested in how you solved the problem with the leaking carb float fuel valve. You eliminated all possibility of fuel leaking around the outside of the valve, so what do you think finally sealed that leak and allowed the float to work as it should?