I have a GW 232 with twin 150's. The starboard motor has no top end. The max RPM I can get is 44 and that is by throttling up and down, if I just leave it wide open I get about 38 RPM's. Here is what I have done so far. I have both engines pulling from the same tank to eliminate the fuel as an issue. I swapped the primer balls between both motors, problem not fixed. Fuel injector assembly was removed and the fuel injectors have been cleaned and replaced the very small fuel filter near the injectors. Replaced the hi and low fuel pumps. All cylinders are firing correctly and the engine idles perfectly. Any thoughts or suggestions on what to do next?
No top end power
- Thread starter Throttle1971
- Start date
When it maxes out do the revs surge and drop or stay pretty much steady?
The former would lead me to suspect fuel starvation, the later would lead me to suspect spark.
The former would lead me to suspect fuel starvation, the later would lead me to suspect spark.
I suppose another possibility is that the throttle linkage isn't opening fully all the time. It could be out of adjustment or there could be a crack in one of the plastic fittings not allowing proper/full range of motion. Compare port to stbd.
Good point. I shudda thunk about that.
It easyto check, take the cowling off and while someone moves the contrail, see if the throttle linkage moves in sync.
It easyto check, take the cowling off and while someone moves the contrail, see if the throttle linkage moves in sync.
What type of engines, 2 stroke, direct injection 2 stroke, or 4 stroke? I have a problem with similar symptoms on my direct injection 2 strokes that I suspect is one of the "mystery filters" in the direct injection system. I replaced my VST filters first and that did not fix my problem. On that note, also check VST filters, I had a fuel injected 2 stroke on a previous boat that had limited RPM caused by a clogged VST filter.
The motors are F150 4 Stroke Yamaha 2005 with 300 hours. I forgot to mention the VST was cleaned at the same time as the fuel injectors. I will replace the plugs just in case that might be the issue but I don't think that is the issue. When I max it out it does surge then the RPM's slowly drop off that is what still makes me think it is fuel related. As I quick check, I will look at the throttle linkages. What would be the easiest component to take off one engine and put it on the other to help to diagnose the problem?
ScottyCee
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IIRC 4400 RPM is somewhere near where the neutral switch (cowling not console) kicks in. Might be worth investigating?
Make sure they replaced the VST filters and didn't simply drain/clean the VST. Those filters cannot be easily cleaned, they need to be replaced. VST filter problems are pretty common after about 10-15 years, regardless of fuel quality.
I agree. clogged VST screen is a common source for your symptoms.
Other potential causes of reduced fuel flow could be fuel pumps. I don't see a screen in the parts in the fuel pressure regulator. Not sure if there is one.
Did you replace the element in the motor mounted fuel filter? ( The filter inside the clear plastic bowl)
If it is VST related, you can't easily swap from the other motor since the high pressure hoses have special cinch clamps that you would have to cut off and replace and you would need the tool to install them. That also assumes you ca get the hoses off without damaging them. The high pressure fuel hoses may not be the same type as the low pressure hose.(it depends on the pressure rating)
Other potential causes of reduced fuel flow could be fuel pumps. I don't see a screen in the parts in the fuel pressure regulator. Not sure if there is one.
Did you replace the element in the motor mounted fuel filter? ( The filter inside the clear plastic bowl)
If it is VST related, you can't easily swap from the other motor since the high pressure hoses have special cinch clamps that you would have to cut off and replace and you would need the tool to install them. That also assumes you ca get the hoses off without damaging them. The high pressure fuel hoses may not be the same type as the low pressure hose.(it depends on the pressure rating)
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It can be the VST for sure, but OP was clear that they were cleaned and filters replaced. I've been fighting mine (cleaned them again this year anyway), and the top end throttle behavior sounds different. Every time I have had crap in the VST filter, the motor reached a certain RPM and then bogged. Leaving it WOT would result in stalling out. It is also rare that would affects just one engine (for long) - especially on the same tank...
The neutral safety switch that is under the cowling is not the one that keeps you from starting in gear. Rather it acts to limit RPM by shutting down cylinders firing to avoid high RPM in neutral, and the limits are about where OP said he was having trouble. It is definitely a possibility that might be explored IMO.
OP - you might consider monitoring the pressure on your fuel rail to see if it dips when you bog. If it does NOT then you need to look at other than fuel starvation. Again, IMO.
The neutral safety switch that is under the cowling is not the one that keeps you from starting in gear. Rather it acts to limit RPM by shutting down cylinders firing to avoid high RPM in neutral, and the limits are about where OP said he was having trouble. It is definitely a possibility that might be explored IMO.
OP - you might consider monitoring the pressure on your fuel rail to see if it dips when you bog. If it does NOT then you need to look at other than fuel starvation. Again, IMO.
Yup - like Freak mentioned, let's skip to the chase and just measure fuel pressure.
Linkages - you're not necessarily swapping... as I noted above, you're simply going to compare and give everything a very good looksie.
Post #2 questions?
Linkages - you're not necessarily swapping... as I noted above, you're simply going to compare and give everything a very good looksie.
Post #2 questions?
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There is a Schrader valve on the fuel injector rail. You need a pressure gauge made for checking fuel pressure, and a hose w/ Schrader adapter. You can buy the whole kit at Harbor freight tool for $19. I did that, and then a month later when the gauge stopped working (shocking!) I bought a nicer gauge on eBay and screwed it into the same hose and fitting set.
All you really have to do to the Yamaha is to take off the cowling and safety cover. You can do it by yourself if you can set the gauge somewhere you can see it from your console.
All you really have to do to the Yamaha is to take off the cowling and safety cover. You can do it by yourself if you can set the gauge somewhere you can see it from your console.
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Have you checked the fuel lines under the cowling for kinks blockages, etc? Had a similar issue. Was a kinked fuel line coming off the under cowl, fuel/water separating filter.
Here is a thought. As I stated earlier the port engine runs great and that is pulling fuel from the same tank however there are still other variables with fuel lines, fuel valves etc. I was thinking of connecting a portal fuel tank just south of the primary ball and see if this fixes the issue. What are your thoughts to this idea and do you think it is worth the effort?
If you are sure the fine filter inside the VST has been cleaned and the fuel pressure at the rail is good, then also look at the TPS voltage with YDIS ($59 on ebay). The TPS is a variable rheostat that tells the computer how to fire the injectors. I had a similar problem with my F150, but at lower RPMs. I feel my TPS had a bad spot in it where the proper voltage was not fed to the ECU. The TPS has to be synched to the throttle body (butterfly) to get the proper fuel air ratio. Not that hard to do if you have a manual. If you don't have YDIS and a manual, you are guessing, it is highly recommended!
The portable tank is a reasonable approach. Bypass the primer bulb also. My gut feeling is that you will still have issues but there are some causes that might allow the engine to run OK on a portable tank. That can happen when one or more of the fuel pumps are bad or there is an air leak. Since the gas level with a portable tank will be higher than gas in the tank, the motor doesn't have to work as hard pumping gas.
The suggestion to measure the fuel rail gas pressure is also a good test but if the pressure is low or varies up and down you will know why your motor is acting up but not what is causing it.
The suggestion to measure the fuel rail gas pressure is also a good test but if the pressure is low or varies up and down you will know why your motor is acting up but not what is causing it.
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ScottyCee
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Wouldn’t you know that it was a fuel delivery issue at that point? That would rule out an awful lot of other causes I would think. But I’m just learning.
Yes but my previous experiences tell me that when the revs surge down and up, it is usually a fuel starvation issues. Spark issues tend to be constant; poor idle or inability to make max power/revs..Many electrical intermittent issues may cause immediate shut down. I guess the best first thing do do as a DIYer is whatever test is easiest to do. Often that is using a portable gas tank but if you have a fuel pressure gauge, that would be a logical test BUT you really need to test under load to be certain that pressure is OK. For me whatever tests I can do without having to disassemble parts is my first step e.g. check the primer bulb, open the tank fill cap, etc.