I'm chasing a problem on my wife's Honda Hawk. I've been fiddling with the carbs, had them off and on several time etc. I need help understanding some choke related things. Here are my symptoms and questions. I know it's not a Monster, but we've got some great mechanics on here and it's pretty basic carb stuff. This bike is only getting about 20MPG and I'm chasing the problem and evaluating everything. Jets are stock pilot and slightly larger (1 size up) than stock for mains because of high flow air flow filter & full Supertrapp exhaust.
Choke operation questions.
1: These carbs have and enrichment circuit rather than an intake air choke. Lever operates smoothly, but doesn't have much resistance. If enrichment circuit is partially open, will it idle high or low when the engine is at a warm operating temp?
2: If the enrichment circuit is constantly adding extra fuel, could this result in the high fuel consumption? I'm getting about 20MPG rather than the normal 35-40MPG reported with these bikes.
3: Would a partially open enrichment circuit cause the running/idling issues I describe below?
Running/Idling/Starting symptoms:
1: Cold starts: AM, about 45ºF or so. Starts & idles fine without using the choke, but choke makes it idle *slightly* faster.
2: Riding at warm engine temp in cooler morning air: Idles lower than should (idle knob turned in quite a bit) but runs ok, but stumbles a bit and is jerky at low RPMs. Higher RPM and wider open throttle operation is quite good.
3: Starting in warmer temps, roughly 75ºF: Starts immediately, no choke and I can ride away almost immediately, but idle/low RPM operation suffers shortly after, just see next item.
4: Riding at warm engine temp in hotter (been around 75º leaving work lately with some stop & go traffic): Low RPM stumble and jerkiness worse than in cooler air with not traffic. At a stop or red light, idle drops off and stalls. Slowing, lots of small backfires from muffler. Holding throttle to keep RPM up and 1500 or so results in a rough idle and a very rich smelling exhaust.
Any insight or basic input is appreciated. I'm trying to look at all options before I tear the bike back apart. FWIW, I've been searching this problem on the web and haven't found much good info, even from the Hawk forums.
Thanks!
JM
IME...
a leaky enrichment circuit will cause low idle when warm and high idle when cold...almost the reverse of a vacuum leak.
The fact that it always starts without the choke tells me it's rich.
What type of carb does the Hawk have?
It does idle higher when cold and much lower (if at all, it usually stalls) when hot.
You mean operational type? It's got a pair of CVs much like my M750. I think the brand is Mikuni but the could be Keihn.
JM
I'd start by checking the enrichment valves for dirt and make sure they're free in the bore.
I'd also consider looking at needle jets....specially if they're Mikuni's. Poor fuel mileage is always a byproduct of worn needle jets
It does sound like those two possibilities. Add sticky float needles not seating perfectly, but you probably cleaned them a few times already.
Enjoying getting the carbs back onto the opposing V4 manifolds? [bang]
Quote from: koko64 on May 23, 2014, 03:27:48 PM
Enjoying getting the carbs back onto the opposing V4 manifolds? [bang]
Yea, that's less than fun... Talk about a real wrestling match!
dp - Hadn't thought about the needle jets, the only has 10,000 miles. I know I gained about 7-8MPG on the M750 when I replaced those. It had about 30,000 miles at that point.
I am going to take the cables off for the enrichment circuit and give them a very good look. The one really stupid thing Honda did was use PLASTIC threaded retainers for the cable ends... Plastic threaded into metal is a recipe for stripped threads.
Koko - I have looked carefully at the float valves as that was my original thought since the carbs leaked. Leak was just bad gaskets turns out. I think they're in good shape now, but will revisit them if the enrichment circuit checks out ok.
Thanks for the input, I'll likely pull the carbs again today.
JM
I'm doing this 1 step at a time. Checked plugs, BLACK. Ok, rich, so easiest step (not opening the carbs yet) first.
Today: Pulled tank, airbox & carbs to assess enrichment circuit & cabling.
1. One retainer was not complete threaded in. This meant that even when the lever was in the off position, the plunger that cuts off fuel for the enrichment likely was unable to seat completely.
2. Other side retainer was finger tight. Probably means nothing.
3. There is a formed two-piece elbow that forms part of the retainer. On one carb, this had gotten separated. This meant the cable for that was (this was also the side that was not fully threaded in) constantly pulled, leaving the enrichment plunger pulled out some, feeding fuel into the enrichment circuit at all times.
4. Other elbow was fine, but at some point (probably last reassembly) the end of the cable at the Y where the single cable from the lever splits into two separate cables had dropped out of its socket. This also could cause the plunger to remain partially out, allowing fuel into the enrichment circuit at all times.
I also took the opportunity to lube both cable ends to ensure smooth operation. I also reattached plungers & corrected elbow joint issue, securing them properly so they can't back off. Secured Y joint of cable to a cable retainer to ensure either of the cable ends could not drop out.
Results (just a few minutes around the neighborhood):
Acted like I expected a cold started motor to. It started without the enrichment circuit, but didn't want to take throttle until the engine had warmed a little. The backfires on closed throttle seem to be gone. The exhaust didn't smell crazy rich sitting in the driveway idling, both when cold and when hot after riding around. I'll run a tank of gas through it and see if that helps the mileage. If not, I'll move to another possible area mentioned above.
Thanks for the input.
JM
Sounds like you might have gotten it. [thumbsup]
At the very least, it's a start. After I run a tank through, I'll know more. Then I'll start checking deeper into the carbs. I'll keep this updated. I know I'm putting a lot of info in each post, but I'm doing so so that maybe it'll help someone else along the way.
JM