Ahhh life...

Questions regarding the DR750

Re: Ahhh life...

Postby H_Lime » Mon Apr 09, 2018 10:39 am

Just wet tested the carbs with engine off. Left carb on the gasket, right one about 3 maybe 4mm or so above it.

Would that be enough to cause a rich condition that wont allow the bike rev past 2k and blow black smoke?

What does the bike run like on one spark plug??
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Re: Ahhh life...

Postby ladder106 » Tue Apr 10, 2018 2:38 am

In what position are the needle clips located? Have you remembered to put the white plastic spacer between the needle and the carb slide with the brown colored spacer on top of the clip?

It's also acting rather like the slides are not raising. Have you perhaps pinched a diaphragm on re-assembly or missed having the spring centered on the carb top?

It is possible to remove the carb tops without taking the carbs off the bike if you have used allen hex screws on the carb tops. A bit more difficult with phillips screws.

With all that, these carbs are supposed to be pretty sensitive to float height but I can't see that 3 mm would be that critical.

Did you really pour 250 cc of oil into the intake tract or am I misinterpreting something?
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Re: Ahhh life...

Postby H_Lime » Tue Apr 10, 2018 2:57 pm

ladder106 wrote:In what position are the needle clips located? Have you remembered to put the white plastic spacer between the needle and the carb slide with the brown colored spacer on top of the clip?


Iirc stock postions Ladder. I only changed one as i bent it on assembly. Im hopeful your hunch here is right and made a balls of the order of assembly with washer and spacer. Would that cause this? She wont pull past 2k and will die if i let go of the throttle.

ladder106 wrote:It's also acting rather like the slides are not raising. Have you perhaps pinched a diaphragm on re-assembly or missed having the spring centered on the carb top?

Im a novice with carbs but thats unlikely but ya never know!! I'll certainly check it.

ladder106 wrote:It is possible to remove the carb tops without taking the carbs off the bike if you have used allen hex screws on the carb tops. A bit more difficult with phillips screws.

With all that, these carbs are supposed to be pretty sensitive to float height but I can't see that 3 mm would be that critical.

Did you really pour 250 cc of oil into the intake tract or am I misinterpreting something?

Yeah left is on the gasket with the right just above it and its so bad i was thinking it was kinda unlikely to be float height surely...

Oil wise i pored it in the inspection covers you do the valves by.
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Re: Ahhh life...

Postby ladder106 » Tue Apr 10, 2018 4:05 pm

Im hopeful your hunch here is right and made a balls of the order of assembly with washer and spacer. Would that cause this? She wont pull past 2k and will die if i let go of the throttle.


The white spacer that goes under the clip (between the metal clip and the slide) raises the needle quite a bit. If you've left that out or reversed the order and put it on top of the clip, the needle would be pushed 3mm or so further down into the needle jet and likely would not flow any fuel as the slides raised.

I was thinking like it was acting as though the slides were not raising or that the needle was somehow too deep into the jet. Leaving out the spacer would cause this. Also a bad diaphragm (holes or tears) will keep the slides from raising as well as a diaphragm that is folded and pinched between the carb top and body.

Oil wise i pored it in the inspection covers you do the valves by.


Whew ! OK.....I though you had somehow poured it into the intake tract before attaching the carbs.


Also - How are you measuring exhaust gas temp to know the gas is too hot?
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Re: Ahhh life...

Postby nug » Wed Apr 11, 2018 11:21 pm

Bit late but..... I do my heights wet and have them set just about on the gasket line. I have found that float (fuel) level does make a big difference to fuelling. Just imagine if the total running fuel depth in the bowl is 30mm, then 3mm to high or low is a approximately a 10% difference in head which can have an effect exactly as a 10% change in jet size will. It of course depends how out of kilter things are to start with but don't discount the difference as if you are at either end of the ideal settings it will make things much worse.
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Re: Ahhh life...

Postby ladder106 » Thu Apr 12, 2018 3:55 am

Here's another potential problem I discovered on my last (yep, just last week) carb rebuild.

The metal tang the contact the main fuel valve letting fuel into the bowl had a decidedly worn spot. This was noted in both carbs.

Looked like this:

Image

Apologies for the slightly blurred image but you get the idea.

Now we all know how little one has to bend these tangs to create large changes in float height. Well....how much "error" does this create? I also thought that these small dimples might also be a reason that a float might "hang" and not drop down correctly to open the valve.

Luckily I had a spare set of floats that were much newer and installed those instead.

That along with some other changes and the bike is fueling much better than it has in a year or so.
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Re: Ahhh life...

Postby batesy57 » Thu Apr 12, 2018 10:24 pm

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Re: Ahhh life...

Postby H_Lime » Sat Apr 14, 2018 6:01 pm

Lads thanks a mill for the advice and as expected it was user idiocy which was the problem.

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As Ladder guessed i assembled both jets wrong. Spring seat below the spacer :crazy: :clap:
Why or how i managed to do this is lost on me but these days i have to keep and eye on the brood whilst working and that and carbs dont mix.
Before trying to start her i reckoned the plug must be fouled.

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Yep.
Swapped them, hit the button and she immediately settled into a nice idle and revved crisply :angel:

Dave, i have to hand it to you man, I've only ran the engine on the bench but its obvious your meticulous work has paid off.
It is as quiet and smooth as i can possibly imagine it could be.
The knock in the crank is gone, theres no gear whine and overall vibration is minimal. I tip my hat to you once more and i owe ya a session in Wales :D
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Re: Ahhh life...

Postby H_Lime » Sat Apr 14, 2018 8:48 pm

Onwards :tup:

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Slight weep so renewed the o ring, oil tight now.

Combine....

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2mm sheet, hack saw, hammer

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Mini compeessor

And you get
Image

Image

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A wee storage compartment compliments of Nugs idea.

Image

Bit of a balls to get at if you consider two battery terminal bolts a bother? Still and all i had to do somthing with the space, was buggin me rightly :lol:
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Re: Ahhh life...

Postby dave#22 » Sun Apr 15, 2018 8:50 am

.............Dave, i have to hand it to you man, I've only ran the engine on the bench but its obvious your meticulous work has paid off.
It is as quiet and smooth as i can possibly imagine it could be.
The knock in the crank is gone, theres no gear whine and overall vibration is minimal. I tip my hat to you once more and i owe ya a session in Wales............

Thank god for that :tup: , the suspense was killing me.
Is it the DR or Capo for Llandovery?
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