carb problems dt 175

[timjam]

Hi , I have a DT 175 79 or 80. Carb is a 2h5. the bike is a us import 2n5 frame number. It runs really flat. Was on a 100 main jet . changed the jet to 130 had a seizure. Sorted that ,still have same problem. Cut exhaust open and cleared out the pipe(it was blocked). no change , still running bad. Will run great with no air filter.have tried less restrictive filter. tried a 120 jet same issue. Bike will run great just off full throttle but on full there is no power and the same thing on half to three quarter throttle.

Any ideas?

[Airhead]

I have seen that some of the American bikes have a restriction in the exhaust header...any comments?

Strip and thoroughly clean the carb, use carb cleaner and compressed air to get it nice and clean. make a note of all the numbers on the parts in the carb jet sizes, main jet number needle and clip position etc, set the float level to 21mm.

[Cynic]

Curious, you have a 1979 DT175 F (US), are you sure you are reading the carb id correctly as 2H5 is closest to 2H500 fitted to the UK version of this bike you should have the ID 2N500.

According to the spec's i have you should be running a 140 main jet. To all intents and purpose the bike is identical to its UK cousin bar some lighting differences.

When you say it runs good just off full throttle and half to 3/4 throttle says that the needle jet is wrong in some way. Too high or in the wrong position, it should be 4 groves from the top.

Also i would be looking at the choke opperation, theoretically it should barely run as it is and even worse without the air filter but you are saying it is flat. And runs better without the filter. Float height may be an issue.

Plug chop thats what is needed i think, so at least we know if we are talking too rich or too lean.