Topic: Honda CB350Four jets for 4 into 1 Mac exhaust

[kmaroon]

For as long as I've had this bike it's run rich and fouled plugs. So much that I've replaced plugs 2-3 times in a riding season. This current round 3 of the 4 plugs are completely black. When I got the bike 2 years ago it came with a Mac 4 into 1 installed on it (not the stock Honda exhaust which is 4 into 4). The carbs were rebuilt at that time, flushed, tuned, gone thru one by one.

Here are the jets that are in the bike now:
35 pilot
78 main

Has anyone had this bike with this exhaust and run into the same problem? What jetting needs to be done to correct it?

Other than this and the usual quirks with 4 carbs, the bike runs great, happy at 50-60mph, gas mileage is around 120 miles before I switch over to reserve. I've put 800+ miles on it since April and 2000 miles last season when some of the big original parts were replaced (chain, clutch) 

[WhyNot2]

Love these bikes, but haven't been able to get mine going to ride it.

I've been able to put only 30 miles on mine since owning it, and that's been since 2007.

It's sitting in the garage, not running now.

Brand new battery a week ago, gas just pours out when turned on.

Have had the carbs off and on so many time.

Gonna be coming off again.

[Bankerdanny]

How do those jet sizes compare to stock? The MAC should not require rejetting. Are the jets themselves OEM Keihin? Does the 350 have adjustable needles? Are they set to the stock position?

[Bankerdanny]

OK, I answered my own question regarding the jets, those are the correct size. So the questions left are (1) are the OEM jets and (2) are the needles OEM and are they set to the correct position?

[carnivorous chicken]

Also check your idle adjust. And what's your altitude?

[carnivorous chicken]

I should add, as well, that you should be able to hold 70-75mph pretty well and under the red line. These things like (and need) to run in the hgh rpms.

[kmaroon]

@bankerdanny - don't know if they are OEM jets, needles were part of the carb rebuild. but it was running rich before the carb rebuild.
@carnivorous chicken altitude is 141, and yes it probably could hit 70-75 but to me that might not feel great haha. It's already really really windy. 

[Trevor from Warragul]

I've owned my 350 Four for about 30 years.  On leaded petrol (gas) it ran perfectly, then, when modern unleaded was all you could get, it began to foul the plugs & display all the symptoms of rich running.  I reduced the main jet size (to 75's from memory), and the bike ran like its old self.

On a side note, with a small right angle screwdriver, you can remove the float bowls without taking the carbies off.  Even better, replace the float bowl screws with caphead screws, and they're even easier to remove.

Trevor