bike not running over 60 - 70 mph

[marcelmot]

Hello everyone,

This is my 1st post, I do not own an Royal Star, I own a Raider and a FZ1. Here I'm trying to help a friend of mine and kindly ask for your help. We live in Romania, Europe.

My friend's bike is an Royal Star, from 2006, with stock air filter and exhausts. The problem is that the bike cannot run faster than 60 - 70 mph, no power in the 5th gear to run faster.

 The bike were imported from USA, it had an accident in the USA and the previous owner removed the cruise control hardware. I don't know if this were done correctly or it has any influence. Also, when high rev the engine, the engine check light comes on. I know this are vaque informations, but I much appreciate any hint.

Thanks

Marcel

 

[BlueSky]

Check the compression on all cylinders to make sure the engine is in good shape mechanically.  Check the exhaust temps to see if all are up to temperature.  It may be running on 2 cylinders.  Check for spark at all cylinders by removing each plug and grounding it against the engine block and looking for spark.  Also, the carbs have rubber diaphragms that have to be in good condition for the bike to get fuel above idle.  

Edited May 14, 2021 by BlueSky

[Freebird]

I agree with the above,.   Certainly sounds like it its not running on all cylinders.  Also check that the boots that connect to the top of the carbs are all seated correctly.  If overtightened, they tend to slip off and suck air.

[cowpuc]

8 hours ago, marcelmot said:

Hello everyone,

This is my 1st post, I do not own an Royal Star, I own a Raider and a FZ1. Here I'm trying to help a friend of mine and kindly ask for your help. We live in Romania, Europe.

My friend's bike is an Royal Star, from 2006, with stock air filter and exhausts. The problem is that the bike cannot run faster than 60 - 70 mph, no power in the 5th gear to run faster.

 The bike were imported from USA, it had an accident in the USA and the previous owner removed the cruise control hardware. I don't know if this were done correctly or it has any influence. Also, when high rev the engine, the engine check light comes on. I know this are vaque informations, but I much appreciate any hint.

Thanks

Marcel

 

Hi @marcelmot in Romania and welcome to VR from Puc in Muskegon Mi USA!! Glad you found us!  If you and your friend on his Royal Star pulled into my driveway and told me of the issue his bike was having and also told me that the bike had been running fine I would have him start it up and let it idle. Then I would put some spit on my finger (or use an infra red temp gun) and check each exhaust header to make sure it was running on all four cylinders at an idle.  If it had a dead cylinder or two I would pull the plugs on those cylinders and check them for spark.. It is not uncommon for these bikes with their small "D" plugs to foul out from over choking,, he may need some plugs..  If it is indeed running on all four at an idle I would pull the carb diaphrams that @BlueSky suggested and check them very carefully for tears/holes. What happens is those diaphrams, by use of  vacuum, control the slide/main jet needles that provide fuel for high rpms.  If a diaphram is torn that slide will not be opening to full throttle causing exactly what you describe. I have actually rescued several Yamahas that were suffering from what you are describing that ended up being those diaphrams but start with the spit check 1st and keep your fingers crossed in hope that it is plugs because those diaphrams can be pricey if they are not repairable...  

[marcelmot]

Thank you very much guys. I read your advices very carefully and after that I have discussed with my friend. He is an old biker and has some experience. 

My friend told me that he already check and all 4 pistons are running, he clean and inspect the carbs 2 times, including the diaphragm and all is in OK condition. Compresion were not done, maybe next step. I told him about the boots, he said are in good condition. I asked him to inspect the diaphragms one more time with a lot more attention, maybe a very small crack, difficult to observe.

In the 1st, 2nd and 3rd gear, the engine has power, but when he shifts to 4th gear and specialy to 5th gear, the bike cannot accelerate more, even going slover.

The cruise control were removed and I don't know if it were done correctly. Can be the cruise control the culprit ? or can have any influence ? as the cruise control has some electronic components ... maybe some wires disconnected or cutted ..

 

Thanks 

Marcel

 

 

[cowpuc]

On 5/16/2021 at 3:40 AM, marcelmot said:

Thank you very much guys. I read your advices very carefully and after that I have discussed with my friend. He is an old biker and has some experience. 

My friend told me that he already check and all 4 pistons are running, he clean and inspect the carbs 2 times, including the diaphragm and all is in OK condition. Compresion were not done, maybe next step. I told him about the boots, he said are in good condition. I asked him to inspect the diaphragms one more time with a lot more attention, maybe a very small crack, difficult to observe.

In the 1st, 2nd and 3rd gear, the engine has power, but when he shifts to 4th gear and specialy to 5th gear, the bike cannot accelerate more, even going slover.

The cruise control were removed and I don't know if it were done correctly. Can be the cruise control the culprit ? or can have any influence ? as the cruise control has some electronic components ... maybe some wires disconnected or cutted ..

 

Thanks 

Marcel

 

 

Marcel, when rechecking those slide diaphrams pay special attention to the area where the diaphram contacts the carb body. A seperation there, under the lip that sets into the groove on the carb body has fooled many carb repair guys. Also make sure the o-ring under the diaphram cover is not missing when putting back together.  Please remember I am coming from experience with the MK1 V-4's, your bike may differ but, concerning the question about the cruise control removal causing this. Assuming your cruise is vacuum controlled as is the spark advance, I wonder if when removing the cruise components, the vacuum source for the spark advance got closed off or overlooked.. Possibly your bike is running without control of the ignition advance... Just a thought.. Puc