97 F650 rejetting with stock jets...how could it have gone so wrong?
 

f650 funduro 97 45000 miles

I bought the bike with 11000 miles on it a few years back. The previous owner had rejetted, cut holes in the air box and put a performance pipe on to match. I didn't think too much of this at the time but... the engine had been running so rich I started to call the bike little piggy. It was backfiring and behaving badly, black smoke etc.. so

I changed the pipe for stock and adjusted (thanks to my friends) the aftermarket jets. but still it was using too much fuel. So I thought why not go back to the original stock jets. I had them installed in January and things were going fine until, the bike sat for about a month while I waited on a new starter switch to be sent from the states. It had started to stall a bit before that, but not too bad. Now the plugs are fouled within a day... black as night, and the bike won't start without a new set put in. I have a good mechanic working on it here and he says the jets are too big and letting too much gas in. He wants to try smaller jets.

Have any of you run into this problem on the f650?

Does anyone have any information on aftermarket jets that are smaller than the stock. I found some info on f650. com website but they were for bigger jets.

also the airbox was modified..... should I go ahead and buy a new airbox and try that?

How about problems with running the engine too lean with little tiny jets? Should I be worried about that as well?

Thanks
Susan

A lean mixture can be very dangerous for any motor. The temperatures go higher and you can easily burn valves etc.
Rather too rich than too lean but then again it should be perfect because a happy engine means a happy biker.
I have never worked on these models before but I will try and help as I understand a fair amount of how the jetting work.

To Start I would recommend that you get the air-box back to original.
A carb will normally have 4 jets all operating different stages of acceleration.
1 - Idle Jet
2 - primary jet - operate when of idle to roughly about 4000rpm
3 - Needle jet + Needle - from 4000rpm to full throttle
4 - Main jet - This jet will only limit the fuel flow at full throttle and because one would only ever run your vehicle at full throttle all the time in racing conditions, this jet will have almost no influence on the carbs performance in normal riding conditions.

The idling jet will have little effect, but there would be no sense in changing this jet so I am sure it will be standard.
On the F650 Carb I do not see a primary jet so I would assume that the next stage will be the Nozzle needle and needle jet. Again there don't seem to be a needle jet but it seem as if the venturi is doing the jetting in this case.
I am sure the jetting problem will be between these two parts that will have to be replaced as a pair and because of the dual carb arrangement it will mean you need two sets.
Part number for the Nozzle Needle - 13 11 2 343 397
Part number for the Venturi - 13 11 2 343 395
Main jet - 13 11 2 343 396
Because I have never worked on this carb before I would recommend that you double check the info.
The idea is just that in most cases only the main jets are changed which hardly make a difference unless if your are constantly racing around at full throttle.
The mixture can also be regulated normally by adjusting the needle position up or down.

Before you do anything make sure you reset the valve clearances!!!!!

Thanks
GS workshop... you've made some good points that I will be sure to pass on to my mechanic..
He has a friend coming from Miami on the weekend and I am hoping that he is able to carry parts down when he comes. My plan of leaving at the end of next week doesn't sound too promising but.... just maybe it will work out.

Cheers
Susan

I'm confused?
 

Susan,

Reading the sequence of posts in this thread, for interest sake, I am confused.
If I get the drift, you have set the jets back to "stock" in January and now you intend to replace them with another standard set (reference GSworkshop's part numbers) OR a set which is smaller (according to what your mechanic wants to do).

I agree with GSworkshop; check the part numbers against what you want to achieve - your initial description of the symptoms = a rich mixture, so that is your start point.

Good luck with the trouble shooting,

Dave

You describe your bike as being fine until it stood for a month .
Therefore I would check that the carb/s [your bike has two if I am correct ?] are not flooding .
Then check the specs and condition of the needles and needle jets because they will have more impact on the running of the bike than anything else .
Your idle jet will function at low rpm and your main jet at 3/4 and above throttle and I personally doubt if either would blacken the plugs at regular running speeds.

There are lots of FAQs at the f650 site which might help
faq.f650.com - /FAQs/

Another thought
 

Come to think of it, is the choke functioning properly??

Dave

Make sure air box is clear.
Good luck.

Hi susan,
Did you post these questions on f650.com?
They are a pretty good bunch over there and should be able to sort out your troubles.
Cheers

I agree with Dodger on this one.
The old 650 has a flooding problem, check Miscellaneous Carb Questions FAQ this might be a problem even if your bike is not leaking petrol.
If you park the bike flat or upphill the petrol will leak into your airfilter and cause a very rich mixture beside the fact that float level is to high anyway.

A friend of mine had a funduro which was almost impossible to start for months.Then it started to leak petrol and the problem was easy to solve.

Thank you all for giving me some good pointers on the carburetors. I'll try and go through and address your ideas.

I will definitely go back to f650 com and check around some more.

It might be that the choke is stuck, but it doesn't feel like it. I have in the past mistakenly kept the choke on while riding the first few minutes, but the high revs would call my attention to that. the last time I rode it was not high reving at all, it was stalling unless I keep the gas on..

The airfilter was a bit dirty but not tremendously so ... It didn't appear to have gasoline in it.

I was really hoping it was just debris in the jets, but that is not what this guy found. He owns 5 Beamers and works on bikes, he is slow and careful, so I just have to trust that at some point somebody is going to figure it out..just maybe it will be him. Plus the nearest shop is in Caracas an expensive 5 hour truck ride away. I hate Caracas, but will go if the bike isn't running by friday.

That aftermarket pipe is 10000 miles away not easily retrieved at this point. and to tell you the truth, I like quiet bikes... I cause enough stir as it is every time I take my helmet off.

Thank you for the pointers on the numbers on the jets and how they are different for different brands. Can this get more complicated? Unfortunately, I left the shop in Caracas without the aftermarket jets they took out..I was in a hurry to get out of the city and now they don't know for sure which jets I had..

I imagine this will all work out and I'll be on the road before I know it. Right?

Cheers then,
Susan

I would just check that you still have a needle in each carburettor. A tiger cub I once had ate its carburettor needle and would only run well with the throttle wide open. Then the floats and float valves. do you have a clean air filter?

Hi Susan.
Yes, someone will figure out what is wrong with your bike.
We know how disheartening it is to have bike trouble while travelling.
If you go on f650.com and post the same info you posted here,there will be many answers.
You do not have to join to post on f650.com, just register. Post your info on the maintenance and mods forum. There is also a member from Venezuela there under the name "SS in vzla". I think he is in Caracas and rides an older, carbed f650. You could try to contact him.

I know I am not much help as my f650 is "fool" injected, and my old beemers have cv carbs, but you may be able to help me.
Do you know if it is possible to put a bike on a sailboat in Puerto la Cruz to get to any of the larger carribean islands like Grenada, or the British Virgin islands, etc?
Cheers, Peter

Hi there,
I see two symptoms possibly caused by two faults:

First:
Bike stalls, does not want to idle (or idles at 2000rpm+) = carbs out of synch.
Forget the BMW synch. instructions (with vacuum gauge) as they only work rudimentally on new bikes but not in real world environments.
Turn the synch. bolt one way and test for result. As far as I remember you have to open the second (operated by adjustment mechanism not by throttle cables) carburettor to prevent stalling and close it if you can't adjust the idle.
Sorry but I did not work on these bikes any more since I phased them out in 2002, my memories have faded a bit.
If things go from bad to worse turn the other way around. Find the area where the engine idles fine without stalling and responds to throttle & goes down to idle immediately and set synch. halfway in between points where things go bad. Sounds complicated but a half skilled mech. will learn it in five minutes.

If the carbs were disassembled adjust the synch. of the butterfly valves visually using the tiny bypass bore inside the throttle body as a mark. This allows the bike to start. Proceed as above.

Second:
Bike runs too rich: This is very often caused by leakages of the float assembly. Note that the problem is very often not the needle valve itself and alone but the little o-rings sealing the float assembly plastic piping against the aluminium throttle body. Replace them with new ones even if they look good and people tell you that they are fine because they ain't. Some fuel aditives seem to cause shrinkage and / or loss of elasticity.

Don't jet leaner than OEM. Never. Rather replace your mechanic.