Generator backfiring and popping from exhaust and carb.

[badkins100]

This is a sweet little Honda EU3000is.  I sent the carb off to Central Maine Diesel to be bored and plumbed for a propane conversion for gasoline/propane/natural gas.  I have one of their bigger (16k) Honda gens which is strictly propane and it's a dream to have. I wanted my little quiet one for those times when no air conditioning is needed. It provides all we need other than central air and a few other 220volt appliances.

I got the demand regulator, some hose, the loading block for the regulator, and my carb back and installed it. Turned on the propane and it fired right up,, but I couldn't home in on the sweet spot to create level running without spitting and popping. I increased the propane supply line diameter,, no change. I bought a new demand regulator,, no change.  It still ran perfectly on gasoline.

Finally, I found this thread here on the OtherPower forum and decided to break into the little red cabinet and check the valve lash.  http://www.fieldlines.com/index.php/topic,129975.0.html

Upon removing the spark plug and setting the piston on TDC, I noticed the rocker arms were still too tight to wiggle.

I adjusted the valves to .006 intake and .008 exhaust and triple checked the gap before giving it a quick try. I also installed a new spark plug and set that gap at .028.  Turned on the gas, hit the starter, and it runs like a sewing machine.

Slight adjustment to the regulator loading block, and I had it lifting it's 3000 watt load just like with gasoline.

It appears that gasoline did great with the valves having no lash. But the propane was apparently getting into the exhaust when both valves were slightly open at the same time, causing explosions at the wrong time and inside the exhaust system and fuel intake. It would blow the little breather loose from it's top clips.  After about half an hour, I could carefully adjust the loading block for smooth running and load carrying reserve. But once the engine cooled off, it took another half hour of the same adjusting to get it to level out also.

Searching for my specific problems left me in a lot of gray areas.  Not being a top mechanic but have rebuilt mower and dirt bike engines and replaced a cam shaft in a pickup, given the engines performance with gasoline, then propane, knowing gaskets were installed correctly, then determining the regulator was not defective, I suspected valve involvement, but doubted it because it's a perfect running Honda normally.  Hopefully my added info will help someone else with a propane conversion which pops out the exhaust and intake and fails to run smoothly.

[just-doug]

i have a portable welder that i convertad to propane.propane requires a smaller spark plug gap,about 20 thousand .a little more spark timing at the start of the advanve curve and the same total number of degrees when fully advanced.valve lash should not need changing.to tight valve lash will ruin smoothness and tork.

[badkins100]

It seemed to run perfectly on gasoline with the tight valve lash,, but with the propane it was pre and post-ignition exploding, throwing pressure and suction on the demand regulator, so it was just going crazy, adding to the problem by going rich then lean in a second. 

It was a research in learning symptoms and cures by a novice internal combustion engine tinkerer.  With all the searching online there were hints of possible problems causing what I was experiencing, and there were lots of advice by all levels of expertise.  This forum, specifically the link I provided, was what caused me to realize I needed to check the valve lash before doing anything else.  I started out with the gaps I listed and was planning to try the others mentioned if it still didn't run just right,, but it ran so good, I left well enough alone.

Honda recommends checking and adjusting valves at every 300 hours.  I see now where that is VERY good advice. I have told all of my friends who own generators to order gaskets and I'd set their valves.  For other novice do-it-U'r-selfers, Jacks Small Engines online has parts lists and make and model exploded views for most small engines. I was disappointed in our local Honda service shop at not being able to work on propane powered generators. I guess it's because Honda doesn't appear to produce them. But I imagine there will be some factory Honda tri-fuels coming in the future.

I live on the grid, but deep in hurricane country, 3 miles into the Gulf of Mexico off Alabama. It's a small island of probably 2000 full time residents.  In my life in the Gulf Coast area, I have endured many times when the power was off after a major storm for a week, and up to 8 weeks one time.  I have been running a gasoline powered 10K Powermate since Ivan and it would run the central air and most everything. I got the little Honda because it will do a lot of things and is quiet and sips fuel.  Last summer, I installed a professionally prepared propane powered Honda twin spinning a 16K inverter gen. and at the same time got my propane company to remove my 100 gal tank and install a 250. The 16k should run around 7 days (+or-) on a full tank of propane. So I figured why run the big gen at times where central air is not being used anyway, such as winter blows that take down power lines. We have had sailboats take down the island feed lines when they broke loose or went into areas they were not suppose to. Both of those resulted in power outage for over 3 days while barges brought in line trucks to repair the broken lines over water.

I switched to propane to end the gasoline storage, handling, treating, and filling operations.  I have to rotate my 50 gallon gasoline supply through the cars and buy new every year even with treating it.  During Katrina, the refineries just to our west were damaged and took quite a while to bring back on line. During that time, I used all of my storage gasoline, 85 gallons from my boat's tank, and since there was huge lines at any station open and you were limited to only 5 gallons.  We had to bug-out to civilization in Oconee Ga. 

Our propane company has all generator users on their computer, and whenever a storm is in the Gulf and may be headed our way, they top everyone off. As soon as the storm is over, they keep everyone supplied with propane. When Fredric hit, it knocked out the old bridge. The propane company brought a large transport tanker full and a bobtail delivery truck.  When the tanker started to get low, another barge showed up with another full load.  So I think unlimited fuel was another plus of converting.

[XeonPony]

make sure to set the valve lash properly! each gen set will be different,


Intake: 0.15mm ±0.02mm
Exhaust: 0.20mm ±0.02mm

Note: Honda publishes millimeters-only for valve clearance specs, because converted decimal inch values can't be precisely used with most feeler gauges. Trying to get "close enough" with an inch spec can result in an engine that is non-compliant with emissions regulations.

-Robert@Honda
Caveat: I work for Honda, but the preceding is my opinion alone.

That was fore my EG3500X from the Smoke stack forum :  http://www.smokstak.com/forum/forumdisplay.php?f=6

[badkins100]

Yeah I had to awaken my novice math mind getting into everything I was reading. I used .006in for intake which is .1524mm and within Honda specs, and .008in exhaust which is .2032mm, which falls within their +or-. I did take a lot of care to set, snug, tighten, and check again, until I got them perfect. They were snug on their proper gauge blade, yet the next size larger wouldn't slid into the lash space,, so I'm there. As far as emissions, I have a great exhaust fan that does away with that.

This is a vast forum and I see several areas that I have interest in. I really want to build a smoke fuel system at some point. That would be good to know.

[XeonPony]

I paid a shop to rebuild my honda as for once I wanted to be lazy, well the SOB's did a piss poor job and it literaly set my hands on fire, I never whent back as I'd have killed them if I did!

the guy never set the valve lash did'nt replace the gaskets I told em five times to do. never checked the valve guids.

for the rockers, use break cleaner on the threads to get the oil off then for the lock nut a drip of rred lock tight, and firmly torque, but not hard! as for the feeler I set it till the right one fits firm with just a hint of drag on removing.

Right now I am working on my 3.0 AJ Onan, right now it is running adiquitely on worn points but I am changing it over to electronic. it was a steal at 200 bucks, put 100 into it to get it run smoothis, new high tension lead, and some chemical cleaners and such.

[Bruce S]

Been watching this thread for some time now.
Thought I'd help explain why you needed to get someone who knew what they were doing with propane engines, or at the very least someone who knows about rebuilding engines for propane.
Propane and Nat'l Gas are both similar to Alcohol in the area of being a cleaner. All 3 will clean out the gunk that's normally built up over time from using gasoline. Once they clean up the residue you'll have issues and valves is one of the biggies. I always hand lapped the engines I worked on, doesn't take that long and you have better control over the lapping process. I've seen guys who say the lapping machines are the next best thing to sliced bread, then go back to find the machines have brunt the guides or faces.
Glad you got it sorted out, this year's winter is looking to be one where people are going to be glad they had some kind of back up.
Cheers;
Bruce S

[badkins100]

They are all running smoothly now,, but you are right about the lapping the valves. I had been reading about it and instantly remembered some older guy showing me how to do that when I was a kid. Probably my neighbor. Made the mating surfaces look like chrome. 

I've been thinking about getting a Harbor Freight Honda clone for 99 bucks and use it as a bench model to learn with,, and while at it, I could make it more durable and more powerful while tinkering. I guess I could use it to replace the little Honda engine in the EU3000 when it blows up,, but I will be 168 at that time and I doubt I would notice the engine blew up.

[dnix71]

I owned a 1972 Pinto. Back in the day, lead deposits protected the cast iron valves and seats, but with the end of leaded gas, the heads had to be redone. I don't remember the exact combo (stainless steel or silicon bronze or both) but the valves, seats and guides all had to be changed and had to match for the engines to run to long.

Propane and nat gas do not lubricate the upper engine like gasoline does. If the engine was not made to propane/nat gas you WILL have trouble if you switch over without redoing the head first. I used to add Marvel Mystery Oil to the gas when I had valve trouble to get me by until the next head job.

With gasoline the valves had to dwell on the seat for a minimum time to transfer heat to the head. With cooler burning alcohol fuels and better materials the valve timing could be changed for smoother idle. The 2.0L Pinto had a minimum fuel octane rating of 91 because of the high compression used to get more horsepower out of a small engine. That made for a rough idle.

With nat gas and propane if the anti-knock rating is lower than gasoline, then doubling the head gasket or shaving pistons to lower compression would take some stress off the valves.

[badkins100]

That may be why Briggs valve lash is recommended set after top dead center.  They recommend bringing the piston up to TDC and keep turning slightly until is has started back down 1/4", then set valve lash. I'm no mechanic here but do know just enough to get me in trouble, and I always set the valve lash gap to the widest gap in the recommended range, or err on the side of wider gap rather than thinner.  Honda instructions were for TDC and Briggs was for just past TDC. If I encounter valve problems, I will have to make some changes. The double head gasket sounds like a fix that is right up my alley.     My generators don't run much other than occasional exercise runs,, but after a hurricane, they could run for weeks. I guess that is when any valve problems could show up.

My dad had a Pinto too. I spent several days under the hood with him.

[Bruce S]

I've been thinking about getting a Harbor Freight Honda clone for 99 bucks and use it as a bench model to learn with,, and while at it, I could make it more durable and more powerful while tinkering. I guess I could use it to replace the little Honda engine in the EU3000 when it blows up,, but I will be 168 at that time and I doubt I would notice the engine blew up.

Just so you know, those $99 units at HF are two-stroke . I have a 25% off coupon and thought about grabbing one too as a just in case. I had some air tool parts to buy ( I use compressed air for cleaning dust out of computers ) looked at the box, then saw the two-stroke label and the need for 50:1 oil. I put it back.

[badkins100]

The one I was thinking of is the 6.5 hp 212cc.  It doesn't mention anything about it being 2 stroke and it has a crankcase oil pan.  They are suppose to be clones of the Honda 6.5 212cc.  They have beefed them up in the past few years with cast iron sleeves, but there are still lots of quality upgrades to make it a rock solid engine.  Ratings on them are pretty good.

[Bruce S]

Got a HF item# on that one? that's sure not what I saw

[badkins100]

They have 2 6.5hp 212cc engines listed.  They had them for $99.00 the other day.

Item # 69730
Item # 69727

[badkins100]

Now, I was talking engines, not generators.  I bet a 2 stroke generator would be a hoot for about 20 minutes.