CB175 K6 carburetor trouble after engine getting Hot

[mhriza]

Hi all,

I am working on my '72 Honda CB175's restoration project.
everything went fine at first, when engine cold start, the engine idled perfectly,
but after a few km riding, some changes occurred in the performance and I notice that the idle it's not as perfect as when it's cold
I Installed the OEM carburetor and make 2 pieces 3 mm insulator for intake manifold. I have tried to clean the carburetor and replace the internal parts with a repair kit, but nothing significant change, my question is,
1. Can heat propagation from the engine affect carburetor performance?
2. Should I thicken the insulator? how thick?
3. or any suggestion for this problem,
Looking forward to hear of you.
Regards,

Riza

 

[RobMan]

With the problem occurring after the engine warms up double check that the valves are adjusted properly and then look at the ignition system as well. Electrical components and connections are heat sensitive as well.

 

[ballbearian]

Hi all,

I am working on my '72 Honda CB175's restoration project.
everything went fine at first, when engine cold start, the engine idled perfectly,
but after a few km riding, some changes occurred in the performance and I notice that the idle it's not as perfect as when it's cold
I Installed the OEM carburetor and make 2 pieces 3 mm insulator for intake manifold. I have tried to clean the carburetor and replace the internal parts with a repair kit, but nothing significant change, my question is,
1. Can heat propagation from the engine affect carburetor performance?
2. Should I thicken the insulator? how thick?
3. or any suggestion for this problem,
Looking forward to hear of you.
Regards,

Riza

That sounds like a possibility. The older (sloper) 175's had long intakes like my 160 but you have a later (upright) 175. Maybe Richard will comment, he knows these very well.
Make sure there is no air leaks once it is warm.

 

[Richard Pitman]

The upright 175s have long alloy intake manifolds. I don't think that heat soak would be an issue. I once left my original 175 idling on the stand on a hot day for several minutes, and was told by a more experienced biker what a silly thing to do to an air cooled engine. That said, no ill effects at all.

And this is the same engine, fitted with CB200 rubber manifolds. Just because I could, no performance advantage. They are slightly shorter than the 175 parts, inlet trumpets on the CB200 air filters are longer to compensate.