1985 Honda 650cs Nighthawk carb questions... Anyone done it?

[Gene]

This is a California-only bike, and from what I've read, has a CARB-mandated lean idle and/or main jet. The symptoms are rough running from idle to approx 3000 rpm. As you might have guessed, it's a bit of a job to take off smoothly, I'm sure some people think I'm a newbie or a wanna-be racer.


Note: I replaced the original paper filter, (NLA from anyone) with a aftermarket foam type which probably made the problem worse.


I've seen several rebuild kits on ebay, with varying parts, I want the complete kits, and probably go up one or two jet sizes on the idle and/or main jet. 


If I'm correct in my thinking, I will need to contact the seller and see if he can supply the larger jets.

[Bob H]

Has it only briefly been run (recently)? Sometimes those things clear out the more they get ridden.
As a diagnostic you could ride around the block without any air filter and that will tell you if the foam filter is contributing to the problem.

I rebuilt the carbs on my NH 750 because I thought a float was sticking, replaced the float needles only to have gas keep leaking. I often work out of state for 6 months at a time, and came to learn that the gas was coming from the pipe that joined some of the carbs, and it was a symptom of having drained the gas before leaving town, it dries out or something. Did that every year until ridden a few times.

[Bob H]

Have you tried adding Seafoam to the gas? A few tanks of that will clear minor clogged jets, but not for a bike that "won't run". It may fix yours.

[draser]

Does it run better with the choke on? Are the plugs white? Had the bike run right before?

I had a Cali bike like that, and according to Partzilla parts list, the jets were the same as the non-Cali. I had to plug the carb air ports but I wasn't able to get them to run right, they were exceedingly rich, plugs were black and it was smoking a lot. I used a different carb rack and everything was fine.

[Gene]

Draser,

My plugs are fine, and it idles good.

An update:

My bike quit running recently, like it was out of gas. I need a fuel filter, and I think I have clogged main and idle jets, everything else is fine.
I tried a Autozone filter recently, but it wouldn't pass gas, (Not in that way). I think the reason was the filter is designed for use with a fuel pump.

When it's running, it doesn't run better with the choke on, except when it's cold. However, a common thing with these bikes is they are cold blooded. Probably because they have a oil cooler.

[mollusc]

Many people have reported problems with added fuel filters.  Maybe one designed for a lawnmower or something might work, but that won't pass the amount of flow needed for a 4 cylinder engine.  There should already be screen filters in your petcock and possibly inside the tank, over the intake standpipe.
Sounds like a tank cleaning and a carb cleaning are your winter projects.

[draser]

The symptoms are rough running from idle to approx 3000 rpm

Gene, if you're running rough at low throttle, how's it running past 3K rpm? Does it smooth out? Because you can't have a fuel delivery problem at low rpm that corrects itself at high rpm.

This is a California-only bike, and from what I've read, has a CARB-mandated lean idle and/or main jet.

Since you're pointing to a lean set up, it'll be good to know if you're plugs are white - to support the lean set up - or light brown or black.

If "plugs are fine" means they're light brown then the lean condition is irrelevant and the slow/pilot jet may be the problem (assuming bike runs fine past 3k rpm).

I think I have clogged main and idle jets, everything else is fine.

Now, it seems your bike runs poorly past the 3K rpm where main jet takes over.

[Gene]

 Hi everyone, sorry for the late reply.

UPDATE:

First of all, it ran fine after 3000 rpm. Plugs are light brown, all four of them.

Right now, the bike is not operating. I am going to remove the carbs, and completely rebuild them. I want to do the job right, and not take any shortcuts. The bike just quit one day, I thought at first it was out of gas. No, it hadn't. I next tried starting it with starting fluid, it started right up, eliminating some possible problems.
I found a source for rebuild kits, they ask everything about your bike, such as stock or modded, stock or aftermarket exhaust, stock or aftermarket, airfilter, etc and then recommend jet and needle shimming changes if necessary.

https://carbjetkits.com/

I'm going to purchase their kit, I will be going richer overall according to their app. I will be glad to be able to start from a stop without having to rev it up to 3000 rpm. People must think I'm a newbie or ricky-racer.

I am also looking at the fuel tank, I suspect some rust because of the present problem with ethanol in fuel.

I luckily have a good friend that will help with the carbs, (He has some chorinated carb cleaner) and he suggested a product that if properly applied, will coat the inside of the tank and eliminate the rust problem.

Fuel Filters: I bought a fuel filter when I first bought the bike. It had too much resistance to fuel flow, I suspect it was for a car with a mechanical fuel pump. I am still researching, any suggestions?

Anyhow, I will report back after my "project" is done. However, it may several months, I'm not in a hurry. (I think)

I hope I covered everything.





 

[Bob H]

Fuel Filters: I bought a fuel filter when I first bought the bike. It had too much resistance to fuel flow, I suspect it was for a car with a mechanical fuel pump. I am still researching, any suggestions?

The petcock has all the filter you need, and all that was considered necessary by the factory. Remove your aftermarket filter.

If there is garbage floating around in the tank, the screen on the petcock is extremely fine - I just replaced mine and was amazed how fine of a mesh it is. Basically you see no grid, no holes.
This is for a 1993 Nighthawk 750, yours will be similar. I replaced mine a few weeks ago because a gas leak had developed (after owning the bike a decade, I start to see constantly wet petcock, very slow drip off of it down to the starter).
I had no idea exactly where it was leaking from, the OEM part is about $200 but Amazon had a knock off for $25 with lots of happy customers. It turned out to the the flattened out O-ring (visible in the photo) where the seal to gas tank occurs.
When I pulled my old petcock, the factory screen was 90% in the tank, did not come off with it. I had to grab it with a pair of pliers and pull it out.
If you get one of those aftermarket petcocks, be prepared to remove 4 screws and re-orient where the vacuum connection goes, as mentioned in many of the reviews. It was easy, and the petcock is solid, no leaks.

[Gene]

Thanks for the replies everyone!

I removed the aftermarket filter, it couldn't have supplied a string trimmer. My petcock is fine, and now thinking about it, the screen was a little dirty, but not much.

Fuel Filters: I bought a fuel filter when I first bought the bike. It had too much resistance to fuel flow, I suspect it was for a car with a mechanical fuel pump. I am still researching, any suggestions?

The petcock has all the filter you need, and all that was considered necessary by the factory. Remove your aftermarket filter.

If there is garbage floating around in the tank, the screen on the petcock is extremely fine - I just replaced mine and was amazed how fine of a mesh it is. Basically you see no grid, no holes.
This is for a 1993 Nighthawk 750, yours will be similar. I replaced mine a few weeks ago because a gas leak had developed (after owning the bike a decade, I start to see constantly wet petcock, very slow drip off of it down to the starter).
I had no idea exactly where it was leaking from, the OEM part is about $200 but Amazon had a knock off for $25 with lots of happy customers. It turned out to the the flattened out O-ring (visible in the photo) where the seal to gas tank occurs.
When I pulled my old petcock, the factory screen was 90% in the tank, did not come off with it. I had to grab it with a pair of pliers and pull it out.
If you get one of those aftermarket petcocks, be prepared to remove 4 screws and re-orient where the vacuum connection goes, as mentioned in many of the reviews. It was easy, and the petcock is solid, no leaks.

[Bob H]

My petcock is fine, and now thinking about it, the screen was a little dirty, but not much.

Sounds normal. Mine was also dirty (photo above) but ran fine - only replaced because of leak that turned out to be O-ring at connection to metal tank.

Putting in those carb rebuild parts will fix you up - I haven't had a need to use them but I think that site has a kit that includes the pilot jets as well as mains. I will run great!

[Gene]

 Thank you everyone for the great responses. I work and have limited time to work on the bike. As I said earlier, I'm planning on removing the carbs and dunking them and then rebuilding them. I got the jet kit, but didn't get the idle jet kit, (sold separately) I am in the process of getting that, plus a gasket set. In the meantime, I'm hoping to remove the carbs soon. I've been doing research, and I suspect I'm going to have to remove the rear wheel, inner fender, air box, and then the carbs. I hope the rubber intakes are undamaged. Whew!

[mollusc]

Shouldn't need to remove the rear wheel.  Unbolt the fender and let it sit on the wheel; that should give you enough room to move the airbox back.

[Gene]

 Never thought of that, thank you.

Shouldn't need to remove the rear wheel.  Unbolt the fender and let it sit on the wheel; that should give you enough room to move the airbox back.