sunnyside

Hi Chuck Thanks for the suggestion. I did check the reeds before, but you are right, I will check again. I now know that I need a magnifying glass to see some of the issues. Not sure if it is my age or the sensitivity of the bike.. This way I noticed a corrosion inside the old needle jet diffusor, as if eaten by the wurms (magnified..) This PHBH carb certainly has an air mixture screw. Its setting seems to have a big effect on the first half opening of the slide.

Hi b40rt It is difficult to know what the gasoline level in the bowl is, but the float level is easy to measure. The spec is 23,5 to 24,4mm. The actual is 24 see also http://www.ducatimeccanica.com/float_levels.html When the gasoline runs out, the level in the bowl drops and naturally the mix gets leaner. The right mix is possibly achieved at a much lower level than the normal level. This phenomena is therefor no sure sign for a wrong float level. I have the bike running now. The problem appears in the idle circuit. When I open the airmixture screw 2 full turns more than the factory setting (1,5), the bike runs much better. I have to test a little more and see the colour of the spark plug, but the bike is very responsive and easily lifts the front again. I expect that with a little more tweaking I get it right. Thanks for all suggestions

Thanks Chuck for the reply. Sorry for the delay, I was travelling for some time. The bike is the earlier version and i am sure the carb is a PHBH. I did see the video before. This is what bothers me. The carb is realy not so complicated, not much that can go wrong, but still.. I found on a German website the confirmation that the jets I have are correct. I now replaced the float, and the jets and the cold starter plunger. Unfortunately there is no improvement at all, so i am clearly missing something. I was doing a test ride with just little gasoline in the tank. When it almost ran out the bike went as it should, so too rich is certainly the issue. The float height is perfect, the float valve new. I am completely lost now. I could buy a new carb, but it frustrates me no end that a bike that ran well before does no longer run because of a cleaning of the carb. I hope anybody has a sugestion for further investigation

Hi again an update. I cleaned everything again and checked all the bits. The vent openings and tube work fine and the tank builds no pressure, which could have been a explanation. I am now wondering if a jet is missing. I see that on the drawing there are 2 jets for the iddle, both in the same channel on top of each other. I have only one jet (the upper I guess). It has a number 60 and it is a diffusor (with a small tube with side holes). Could it be that this particular bike only uses one iddle jet, or could it be that I lost the other jet? In that case does anybody an idea what jet I should try? Any suggestion is much appreciated. Joop

Hello everybody I am a first time user of the forum and this is my first experience with a trials bike. I have however a long experience with bikes in general. I have not seen any other item on the forum, so I hope someone can help me a little further. This bike is from a friend of mine. He asked me to look at it and I can use it so now and then when it runs again. The bike was always running very well and nothing has been changed to the bike, apart from what I describe below. When I got the bike it had not been used for over a year and it wouldn't start. Obviously the carburetor was all gummed up, so I cleaned it. When I put it all back together the problem started. The bike starts well, but reacts badly at the throttle. Slow response and does not run high. (I think this is called 4 stroking) Lots of smoke and the ends of the overflow tubes are wet with gasoline. They however do not "flow" The spark plug is wet, but I have not run it for long. My conclusion is that the mixture is (way) too rich. See below for the details and for what I did and tried. (the obvious float height, float valve and cold start system) Nothing has however made any change to the problem so far, not even dropping the needle 2 notches. I now plan to change the needle and jet, the float with the valve and the plunger of the cold start. These all however seem to be in good working condition, so I am a little lost and do not expect this will solve the problem. I therefore would like to hear if anyone on this forum has ideas on what else to try or look for. The bike is a Montesa 314 R The carb a Dellorto phbh 26 SD clip on 3rd groove from top jets: Needle X6 needle jet BN 264 main jet 97 cold start jet 60 iddle jet 60 float bowls white, connected, 9,5 gram type 9010.1 float valve 200 airscrew 3/4 out Sparkplug BPR5ES (also tried without resistor) Can anybody confirm this is all correct? Carburettor body and jets cleaned with ultrasonic all seals replaced with new. Float height is 24 mm, welding line is parallel to carb body. Float weight is 10 gram on my scale, but it only measures in full grams, so could be anywhere between 9,5 and 10,5 grams Floats are opaque, but I cannot see any gasoline inside. No sound when I shake. The float valve seems to close well when I blow on the gasoline tube. The rubber tip looks ok. Cold start plunger seats firmely on the jet when closed. New sparkplug and old spark plug, both same bad result. The needle has small wear marks. I dropped the needle by moving the clip to the upper groove (2 notches up) and the engine still seems to run way to rich. (4-stroking) I hope anybody has a suggestion.