Hello Team

For some time now I have been struggling with lack of power and having to run with full choke on my 3800.

I have rebuilt the engine with new gaskets to try and eliminate air leaks.

I noticed that the fuel is returning in bubbles not a solid stream so I now think maybee it is a petrol pump problem and not the crank seals.

Any ideas what might be causing these bubbles?

Cheers

Matt

Hi Matt,

The bubbling in your clear return pipe can be caused by a few things. It can be that you're fuel pipe is to close to the exhaust. This heats up the fuel which gives the problem you are struggling with at the moment. In the summer such problems appear, because of the higher outside temperature in the summer. (here in Holland we have bad weather so no solex riding at the moment)
This can be solved by bending your fuel pipe away from the exhaust.

You can also check if your fuel pipes are good connected, if it sucks false air you have the same problem. Can be solved bij tighten up the nuts that connect your fuel pipe with carb and fuelpump.

Another solution could be that your fuel pump doesn't has the capacity to pump enough fuel to your carb. Can be the pump itself or the pumpmembrane.

Maybe this answers could help you solve the problem,

Kind regards,
Rob de Jonge

The observation of the bubbles is not dramatic.
at least this shows sufficient fuel is available to return to the tank.

Use compressed air to blow out your main jet of the carburettor.
Check whether the compression ratio of your cylinder is still OK
( the lower the ultimate compression th richre the fuel/air mixture needs to be to combust)

Also check the timing of your ignition, do not rely solely on the markings ( flywheel marking versus crankcase marking) but actually measure the advance of the ignition by using a vernier calliper through the spark plug hole. Pre ignition should read about 2 mm ( not in Inches)

Hi Rob and Joan

Ill give you a little history on my 3800.

About 20 years ago it was my daily ride to school. At this stage it was very lucky if it got its tires pumped up let alone any routine maintenance - yet it refused to die and always just kept going very well (33-35 Km/H on the cycle computer).

About 5 years ago it got pulled out of the back of the garage for an annual moped rally of about 80Km. It got a wash new fuel and the tires pumped up. For three years it went fine.

2 years ago it developed the fault of no power full choke. I thought this most likely to be faulty gaskets as opposed to the crank seal due to how sudden it was.

What has been done and checked.

1) Barrel honed new piston and rings (Shorter MBK piston)
2) Checked jet was running a 30 cc Now running 32cc
3) All gaskets replaced.
4) Everything De-Coked (calamine??) except for the exhaust pot.

Still to do
1) Rebuild pump with new membrane.
2) Clean points/Check timing.
3) Cook the exhaust pot on the BBQ.
4) Ride it on a cold day!

Some observations
1) Going up a jet size did make a small improvement.
2) It runs worse/requires more choke the hotter it gets.
3) The choke setting does not seem consistent even on a flat level road.
4) The fuel flow does not seem consistent. Some times there are no bubbles some times there seem to be a lot.

Have you ever heard of a sudden failure of a crank seal due to lack of use?

Ill report in once I have rebuilt the pump and taken it for a ride.

Cheers

MattO

The fact that you have to run on a 32CC mainjet is surprising, standard is 28CC

Most probably there already was something very wrong.

When these high jet numbers have to be used it tells something on the combustion and apparently you need an extreme rich mixture ( unless the carburettor is altered from the standard 6.5 bore to an extreme 10mm, if this is the case check the outlet
from the fuel mixture chamber into the main bore, this is the so called "venturi"tube a smal brass tube pressed into the die cast body of the carburettor.

Another occurring mishap, frequently not taken into regard is the "rot" of the crankcase alloy.
Thoroughly clean, check for pinholes and apply a coating after cleaning.

Check pre-ignition ( about 2mm BTDC) and check the compression release valve for tichtness ( regrind the surfaces to each other)

I think the same Peter, the pump diafragm could be dried out.
It's a relatively cheap part, and ain't much work to replace. Maybe you should do that first before adjust your timing and bake your exhaust. Also clean the pump good so there is no dirt or something in it. So you can be sure that if the solex has the same problem after this, the problem won't be your fuel pump.

MvG
Rob

Hi Team

I have fitted a new pump membrane with a very slight improvement. It was cooler than last time I rode the bike.

I am still running the 32 cc main jet and now require slightly less choke (half choke previously 3/4). Speed is 28-30 Km/H which seems a little low.

I soaked the pump in petrol for a week while giving it good shakes to get the crud out.
I ran a wire through the fuel pipes to make sure they were not blocked.
I ran a fuse wire through the carburetor venturi.
Decompression valve ground in.

The 32cc main jet still seems way to big. It is still running the standard 6.5mm carb

-I plan to put the piston at the top of its travel and fill the crankcase with petrol and look for leaks (about an hour???)
-Remove reface and retime points.
-I have a new exhaust on order so will fit that when it arrives( Impex).

Any further ideas of things to try??? I am starting to convince myself it is the crank seals (A bad thing to do with no proof!!!).

Merry Xmas (Please Santa can I have a magic bullet for a 3800!)

Cheers

MattO

A new exhaust will increase your speed i think, dependig on your previous exhaust. When my solex came a live after 30 years doing nothing the new exhaust increased the speed up to 34 km/h. Now I have a new cilinder and piston and it runs even faster now.

MvG
Rob

Hi All

Thought I would give you a small update.

I put some petrol in the crankcase to test the crank seal. As fast as I could poor petrol in it came out

I have rebuilt the motor with new double seal bearings and a new crank seal. It now passes the above test and is not leaking.

The crank has no positive form of location in the block. How close do you have to get it in position? Will it find its natural position over time? I think I have it pretty close and the motor turns freely.

In New Zealand it is winter now so cold riding and night is tne garage are not very appealing.

I will report in once I have taken it for a ride. Hopefully all goes well and I have some more speed and cure the choke and jet problem.

Cheers

Matt

[quote=Joan][quote=Matt]Hi All Thought I would give you a small update. I put some petrol in the crankcase to test the crank seal. As fast as I could poor petrol in it came out :( I have rebuilt the motor with new double seal bearings and a new crank seal. It now passes the above test and is not leaking. [color:#FF0000] A new double seal bearing will not last very long because the two stroke mixed lubricant has no acces to the balls of the bearing and the lubricant of the bearing will be leached out by petrol vapor. [/color] The crank has no positive form of location in the block. [color:#FF0000]It does have, it is very stuck on the crankshaft axle a so called negative fit and when fitted into the crankcase it should have a forging of the crankcase around its perimeter ( engine type 3800), actually a once in a lifetime construction not intended to be repaired [/color] How close do you have to get it in position? [color:#FF0000]If it is not in position either the big end will jam into the crankcase cover ( to far to the right and also the flywheel may be obstructed by the ignition coil scraping it of and rendering it un usefull [/color] Will it find its natural position over time? [color:#FF0000]Never, there is no little pigmee in there that does the job for you [/color] I think I have it pretty close and the motor turns freely. [color:#009900] [/color] If it is not in good position it will not turn freely for long. please check it. In New Zealand it is winter now so cold riding and night is tne garage are not very appealing. I will report in once I have taken it for a ride. Hopefully all goes well and I have some more speed and cure the choke and jet problem. Cheers Matt [/quote] [/quote]

Aan John Meisters:

Wat is de bedoeling van bovenstaand bericht ?
Je gebruikt het originele bericht om the "quoten" maar verder gebeurd er niets alleen de kleurstelling is verdwenen en nu zie je het verschil niet meer tussen aanvulling op het originele bericht en de eerste tekst