Hobbit won't rev part deux

I have completely gone over the Hobbit pa I.

Completely cleaned the carb including the emulsion tube. Verified float height. Pulled entire exhauset system and cleaned exhause port , muffler and muffler tube. Hobbit just won't rev up without breaking up. Even installed new plug. Checked for gas in float bowl and it's full. I can get about 10mph but the bike starts to rev it breaks up. Am I looking at a condenser problem or what. I'm very close to pulling the very big sledge hammer out and when I'm thru dragging it to the corner for trash. Maybe I should charge a buck a hit and recoup my expenses. I'd appreciate ANY reasonable thoughts on this. Time is running out for Hershey...

Re: Hobbit won't rev part deux

if you suspect ignition, have you checked the timing? are the points contacts bright and clean and square? go through Freds Guide for more ideas..

if you have good, working spare parts to swap, like a condenser or ignition coil / plug wire, try it after you've gone through all the normal tune-up stuff.

Re: Hobbit won't rev part deux

Joew: I think I am getting closer to finding the problem. The ped won't rev or have any power even when you pull the air cleaner element and the exhaust. I looked at the new plug and it was loaded with gas? I did a basic compression test putting finger over spark plug hole and cranking pedals and got almost no /zero compreesion. I pulled the head and found minimal carbonizing. I pulled the decompression valve and no carbon on valve face or the seat. The cylinder walls look great? Head gasket intact. So...either it's rings, reed problem (which I know nothing about) or crankcase gaskets? Any ideas? The plug loading up with gas has me puzzled. The float is set correctly and I actually checked the amount of gas in the bowl and there was plenty but not too much so the needle valve is working correctly. Geez..ideas..can I still get rings and stuff for these?

Re: Hobbit won't rev part deux

reed is easy to check.. Its just a flat, flexible metal petal that seals against a rubber "gasket" thing. If the petals are bent or cracked it could leak. But that wouldn't affect compression. Compression only involves stuff above the piston (rings).. nothing below in the crankcase matters.

Double check the decompression valve and make absolutely sure it seals.

Look for a badly warped head surface or a cracked/broken/whatever head gasket.

Are the rings carbonized-stuck in the ring grooves? If so they wont seal.

You got a hole or crack in that piston? probably not or you'd see it.

Not a lot of things can cause zero-compression.. hardest to detect is bad rings. Squirt some heavy oil around the piston and try again. The oil should seal the (bad?) rings and then show some compression.

----------

I tried Honda for rings but no luck. And, in my experience, they aren't gonna lift a finger to help you find a Honda ring from some other bike that would work.

First find out how the compression pressure is leaking away..

Re: Hobbit won't rev part deux

Pull the cylinder and check the rings then let us know.

Re: Hobbit won't rev part deux

while we're at it, may as well mention a couple other far-out possibilities...

Examine the head for cracks.

The spark plug itself and it's threaded hole are potential places for a leak.

When you check for compression, some air must be allowed into the engine or there's nothing to compress.. Was the throttle open? Could something be preventing air from getting into the engine even if the throttle is open? (Like did you ressemble the reed valve cage upside down or leave a oil rag stuck someplace inside?)

my guess is it'll be the rings but coming up with weird possibilities is somewhat entertaining.....

Re: Hobbit won't rev part deux

I'll pull the cylinder. I have a friend who owns a huge Honda dealership I'll call him tomorrow and see if he can come up with a set of rings. Thanks for all your help.

Re: Hobbit won't rev part deux

what do you guys think about the wet spark plug?

Re: Hobbit won't rev part deux

fuel is pouring into the engine, wetting and fouling the plug .. only place it could come from is the carb.

Here's a thought.. Suppose that only a very small amount of air was being allowed through the airfilter / intake box .. compression test would likely read very low while a very rich fuel:air mixture was delivered to the cylinder.

Have you examined the air box? Are the 3 little holes in that rubber intake tube clear? More than once people have found wasps nests, bee hives, dust bunnies and/or a litter of dead meeses in these boxes.

Re: Hobbit won't rev part deux

Joew: The rubber triangular tube that has three equal sized holes in it? Is that what you're referring to? I shined a light down into the tube and looked as best as I could and I couldn't see any obstructions. Do you recommend pulling the carb (I'm getting real good at this) and actually removing the tube and investigating lower part of air box? I'll check your answer later. Thanks Wardie

Re: Hobbit won't rev part deux

Air restriction could be the problem, causing a constant rich mixture (similar to the choke being always closed). If the holes are clear, remove the filter element and look up inside the box. Get a coat hanger and hook it around and see if something found a home in there.

gotta go about this in a systematic, logical manner. Eliminate the possibilities one at a time. You've already done a lot cleaning and adjusting.

btw, am i correct that this bike never ran right for you?

and is this still true?

_ it starts fine but as soon as you get it going it starts to bog, lose RPM and never really get going_

This symptom (combined with the wet plug) has all the markings of carburetor mixture trouble.. specifically a rich mixture.

Re: Hobbit won't rev part deux

You are correct I bought it this way thinking it was a simple clean the carb deal. Oh what a mess.

Re: Hobbit won't rev part deux

well.. since it never ran right for you nothing can be assumed. Fortunately that bike is about as simple as they come and solidly built.

Serious internal mechanical damage or weird ignition trouble is unlikely. After all, the thing does get to 10mph.. and it's already known the spark plug is fuel-fouling.

Have you done a proper compression test? (Throttle open .. using a more reliable gauge than a thumb in the plug hole.) If so, might the rings stuck in their grooves? Did a squirt of oil around the piston's crown improve compression?

This and all the other basic things (like a clear air intake) have to be checked and eliminated as reasons the bike won't rev..

Re: Hobbit won't rev part deux

Thanks Joew: you've been a big help. I am going to unbolt frame, pull carb and pull that darn rubber snorkel..check everything including the intake. Suiffice that I was able to purchase new standard rings, head and nase gasket. I have Friday and Saturday to get it done then I'm off to Summit Point Raceway for Thunder Bike Weekedn. Have a nice Memorial Day and I'll keep you posted. Wardie

Re: Hobbit won't rev part deux

cool.. i guess your honda friend came through.

as far as unbolting the frame for carb access.. THIS outlines the method i prefer. Suspending the frame and disconnecting the shocks isn't required.

Re: Hobbit won't rev part deux

Jason Luther /

having someone help hold it is key, as mine took a two foot fall of a bench. miraculously nothing was damaged or broken. i have sense cut two 1x2's to the proper length and can wedge them under the rear chrome rails and up under the rear fender, that holds everything quite snuggly. i still cant believe nothing broke in the fall, and strangely enough got 5 more mph (just kidding)

carb removal

i welded a little angle-iron stand to hold the bike.. a short pipe fits in / under the fork tube and raises the front wheel off the ground. But lately everytime this carb access comes up i stare at the bike for a while.. wondering how to modify it.

so last night i'm thinking that if just the top part of the airbox were removable (where the rubber air horn goes) the carb might be able to come out of there.. gonna take a closer look and measure some stuff today..

btw.. you really want an extra 5mph? i haven't tried it yet but i think it'll work.. see pic.

1117221868_pipez.jpg

Re: Hobbit won't rev part deux

Joew: No obstructions in air snorkel or air box. Purchased new needle valve. As I write this I am soaking the carb and will reassemble for the umpteenth time. I am checking the reed valve for closure then it's on to the rings. My Honda manual shows two rings. The rings that I got from Honda have a top and bottom ring and the top ring uses an expansion ring behind the upper ring. The shop mechanics said that's where it goes but the fiche and my shop manual don't show any expansion ring. Have you had experience with this? Man when I get done it'll run good and then I'll quit my job and become a Hobbit mechanic...ha

rings

expander? never heard of such a thing.. can't even picture what you mean..

is it like part-A in this pic? A spring or something behind the top ring?

As far as the carb, make sure the brass tubes (and their pathways) in the air intake horn are clear. Remove the idle speed screw to access that other screw below it. Remove this cover screw and air-pressure blow the passages out. There's a tiny jet in there so don't stick anything sharp down in the hole.

On reassembly, to avoid vacuum leaks, i like to use something like Permatex 2 (non-hardening gasket sealant) on the reed block and intake manifold gasket surfaces.. the area is prone to leak.

Avoid it if at all possible.. but if you must remove the reed petals from the reed block, a touch of blue (temporary, removable) Loktite is needed on the tiny screws when reassembling..

Re: rings

it is exactly as pictured. The Honda mechanic said he thought he remembered that the wavey ring goes under the top ring? Do you remember how it went? When I pulled the cylinder off and checked the rings there was no wavey ring under either ring? Can you shed some light on this. Also the block that holds the reed valve was just sitting there loose on the motor. I think I will put #2 Permatex as suggested on its base.

Re: rings

huh? the reed block was sitting loose on the engine block? It's supposed to have four fat Phillips head screws holding it down. They are M9x1 threads.. two short ones 25mm long and two longer, 40mm long.

afaik, the Hobbit rings are plain rings and have no expander behind them. No Hobbit / PA50 owners ever mentioned such a thing in these forums to my knowledge. I wouldn't use it.

what the hell's up with that reed block.. no doubt in my mind that if it's not fastened down it could cause your problem.. easily. Maybe that's it.

Re: rings

no it was fastened down when I removed carb and screws it was loosely sitting there no permatex is what I meant. I went to MRA site and guess what they show a ring expander on the lower ring . Check it out. So much for the hONDA MECHANICES MEMORY.

Re: rings

well.. if you're intent on using it pay particular attention to the cleanliness of the ring groove.

A ring needs space behind it. The expander will occupy some of that space. A carbon layer or particles in the groove could force some portions of the ring into hard contact with the cylinder wall.

Ring grooves should not be scraped clean with a sharp tool (like a broken ring). Aluminum is soft. Any scratches or other damage to the lands means a bad seal. It's better to soak the piston in solvent and carefully remove any carbon with a soft bronze wire brush or similar.

I hope for your sake the expander belongs there.. just can't think of a reason extra radial tension would be needed. But ya learn something everyday if you keep your eyes open.

Re: rings

Joew: With the expander on the lower ring you can't safely compress the rings to push the piston into the bore. Maybe the fiche showed a newer model but it definitely won't work. Now that I've tested the new rings the same problem is at hand. Spark Plug loads up. On the advice of a friend I put another spark plug cap on. The plug has a white spark not blue so I'm not certain if I have a problem there. The coil checks out? Funny thing I was playing around with it last night and thought well I'll shut off the gas and the darn thing actually revved up when it was near ouit of gas? Workin' towards a solution..any thoughts on the coil and spark plaug cap and the gas thing?

Re: rings

diagnosing ignition components is just plain tedious and near impossible without the tools and specs and knowledge .. i'd much prefer to swap out suspected parts. I assume you did all the regular tuneup stuff already, points clean and timing adjusted, wiring checked, etc. .. no questions and everything ignition related seems ok on it's surface?

As far as rich mixture, something else comes to mind that i dont think has been brought up. This carb relys on precisely premixing air and fuel above the main jet inside that emulsion tube chamber. Air is fed into it through one of those brass tubes in the intake horn. If the air pathway were clogged up you'd get a very rich mix. I know you been through that carb a couple times already.. just though i'd mention it since this still sounds like carburation trouble to me.

carb mixture

For what it's worth, here's basically how this carb works.

There are two brass tubes inside the intake horn. Air enters both.

Idle:

One tube, on the choke-lever side (right side of the bike) is idle air supply. There is a tiny fixed idle-fuel jet in this pathway below a protective cover screw. Incoming air causes a venturi effect and draws idle-fuel up from the emulsion chamber and through that idle-jet.

This fuel mixes with the air entering the air tube. This too-rich mixture then goes forward past the idle air/fuel mix adjustment screw where the rich idle mixture can be metered and leaned out with more air. The adjusted mix is then finally sprayed into the butterfly-throttle area.

-------

Running fuel supply:

The larger, longer brass inlet tube (left side of bike) is the one that provides emulsion air for normal running. This tube's air goes directly into the top of the emulsion cavity.

Fuel rises through the main jet and into the perforated brass emulsion tube. Air is allowed in through the perforations.

This premixed bubbly fuel/air mix is then sucked up into carb's venturi and into the engine.

On this style of carb (butterfly) it is vital that the larger fuel droplets be broken down into a mist. The emuslion tube does this. If enough emulsion air is not supplied the carb will deliver a very poor mixture that wont burn well... Drops of fuel will likely foul the spark plug.

So, not only is fuel mixed with the air coming into the carb's large throat, fuel and air must also be premixed inside the emuslion tube cavity..

Re: rings

My unit had the same symptoms. Check to see if the carb float bowl in on properly. It can be installes 180 degrees out.

Take off the right side chain cover. Look thru one of the cut outs in the chain sprocket. There is a hole in the engine mounting cheek that allows access to the float bowl drain.

If you cannot see the drain screw, take the carb out and reverse the bowl.

Your wet plug syndrome could well be caused by the improperly installed float bowl. This will pinch the float and not let it rise to shut off the fuel.

Good Luck

Re: rings

Joew: What does afaik mean?

Have second carb soaking all night and will blow dry tomorrow and replace current one on the bike. I finally received my floorboards from a guy in Canada and repainted them in anticipation of eventually getting this Hobbit going. Last night for just a couple seconds I actually heard the engine rev to full power. I watched the variator wind up the belt and it was all cool unfortunately it was all too brief. Well it sure has good compression now! Let you know what happens. Have you ever seen the spatrk plug caps go bad before?

Re: rings

afaik = as far as i know

if that rev-up was due to the engine running out of fuel (and so leaning out) i made a comment about that in the other thread.

plug wires carry a very high voltage. The wire is thick and heavily electrically insulated so the spark doesn't short circuit before the energy reaches the plug's tip. However, insulation does break down eventually .. spark energy can then leak away. If the plug wire or boot is deteriorated and has visible damage it might contribute to a weakened spark. Moisture or dirt or grease can short circuit a spark. The boot should fit snug on the plug's metal end. Plug wires and boots are worth some attention.

Re: Hobbit won't rev part deux

Joew: Swapped the carb and it ran to 15mph indicated on speedo . Gas is leaking from carburetor overflow sound I'm pulling it agin and adjusting float level. It still seems like it isn't pulling under a load as much as it should.

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account